It covers all the aspect of pulsatility in Endocrinology including physiologic features & methods of analysis

1. Pulsatility in endocrinology
Dr. Shinjan Patra
D.M. (Endocrinology) Resident
All India Institute of Medical Sciences
Jodhpur

2. R/F for Pseudomonus infection
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4. Pulsatility in endocrinology
Dr. Shinjan Patra

5. Contents
• Basics of Pulsatility
• Types of Pulsatility
• Pulsatile features of various hormones
• Pulsatility measurement challenges
• Altered pulsatility in patho-physiology
• Analysis of pulsatility

6. Introduction
• Physiological experiments beginning in the 1970s
demonstrated that secretion of the majority of
hormones occurs in a pulsatile manner
• Understanding exactly how pulsatility arises, and
how it is propagated in the patterns of downstream
products, has proven to be very difficult
• Established unequivocally after the development of
RIA methods

7. Pulsatility- Definition
• “Pulsatile” denotes the recurrence of individual
punctuated events (bursts, peaks, or pulses)
interrupting a more or less constant baseline
process
• A pulse is identified by an abrupt increase and
subsequent decrease in the intensity (size or
amplitude) of serially measured output
• In principle, the size, shape, and spacing of pulses
may be regular or variable, and the underlying
baseline process may be fixed or drift gradually

8. Examples
• The most common cellular products observed to
be released in this manner are intercellular
signaling molecules such
as hormones or neurotransmitters
• GnRH/FSH/LH
• GH
• TRH/TSH
• ACTH/Glucocorticoids/Mineralocorticoids
• Insulin
• PTH

9. Other systems
• CNS- Oscillatory activities in pacemakers &
central pattern generators

11. Basic Endocrine Importance
• Development
• Growth
• Reproduction

12. Neuro-Endocrine Pulsatility
• Nervous system control over hormone release is
based in the hypothalamus, from which the neurons
that populate the periventricular and arcuate nuclei
originate
• These neurons project to the pituitary gland via
the hypophysial portal system and dictate endocrine
function via the four Hypothalamic-Pituitary-
Glandular axes

13. Time-Scales of Pulsatility
• Ionized ca conc exist within single endocrine
cells with periodicities of milli-seconds to
seconds
• Vasopressin/Insulin/Glucagon/PTH- 4-30 min
• GH/Prolactin/Gonadal/adrenal steroids- 45-
180 min
• LH secretion every 3 hours in late-luteal phase

15. Types of Pulsatility

16. Amplitude Selective control
• The size of pituitary-hormone pulses, defined by
amplitude (height in concentration units) or mass
(amount secreted per burst per unit distribution
volume) can vary by as much as 1000-fold in the
same individual on the same day
• Ultrasensitive CLIA assays reveal awake daytime
food suppressed plasma GH concentrations of
0.012–0.035 g/L and sleep- and fasting-
augmented concentrations of 8–20 g/L

17. • Less profound amplitude-selective modulation
applies to insulin secretion. Pulse-size
variations are 2- to 7-fold in diverse path
physiologies, such as aging, type II diabetes
mellitus, renal failure, obesity, and physical
deconditioning
• Two- to 5-fold variations in secretory-burst
mass typify PTH, aldosterone and cortisol

18. Preferential frequency control
• Reported for oxytocin pulses in parturient and
postpartum women

19. Combined amplitude & frequency control
• LH- The prototype example
• Achieved by way of negative feedback by gonadal
sex steroids on the amplitude and frequency of
the GnRH pulses and the amplitude of LH
secretory bursts
• The degree to which basal (non-pulsatile)
hormone secretion is regulated is not known
• Ignorance in part reflects earlier technical
uncertainty about the valid estimation of true
basal secretion
• Other- FSH/Prolactin/Gonadal sex steroids

20. Triple Control
• The size (mass), number (frequency) and shape (waveform)
of ACTH and TSH secretory bursts regulated
• Cortisol depletion augments ACTH secretory-burst mass by
9.6-fold, increases ACTH pulse frequency by 1.25-fold, and
abbreviates ACTH secretory bursts by 1.5-fold
• TSH secretory-burst size and frequency increase by 2.0-fold
and 1.2-fold, respectively, overnight, whereas the time to
maximal TSH release within a burst decreases by 1.5-fold
• These nycthemeral changes are selective because the
quantifiable regularity of the ACTH and TSH-pulsing
mechanism does not vary over 24 h

21. Pulsatile features of various
hormones

22. Hypothalamo-Pituitary-Gonadal Axis
• Single pulse of GnRH stimulates the release of
both LH and FSH
• Due to some divergence between FSH & LH
secretion, there is believed to be a separate
factor which can cause secretion of FSH

24. Mechanism
• Ensemble of GnRH neurons in the
hypothalamus that send axons to the portal
blood system in the median eminence fire in a
coordinated, repetitive, episodic manner,
producing distinct pulses of GnRH in the portal
bloodstream
• GnRH neurons show a bursting pattern of
electrical activity

25. FSH vs LH
• Simultaneous LH pulses in peripheral
circulation
• Pulsatile LH is used as an indirect measure of
the activity of the GnRH secretory system
• Secretion is not always pulsatile
• Even when it is pulsatile, there is only partial
concordance between LH and FSH pulses

26. Basic Clinical Implications
• Different frequencies of GnRH can lead to
different ratios of LH to FSH secretion from the
pituitary
• Slower pulse frequency (one pulse of GnRH
every 3 hours) led to a decrease in LH
secretion but an increase in FSH secretion so
that the ratio of FSH to LH secretion was
greatly elevated

27. Physiology in Menstrual cycles
• During the normal menstrual cycle, LH pulse
frequency increases during the follicular phase
as the midcycle ovulatory phase is
approached, reflecting increased GnRH
pulsatility
• Slows during the luteal phase

30. Modulation of Structural make-up
• The extent of glycosylation of LH and FSH is important for
the physiologic function of these hormones
• Forms of gonadotropin with more sialic acid have a longer
half-life
• Slow frequencies of GnRH, seen during follicular
development, are associated with greater degrees of FSH
glycosylation, which would provide sustained FSH support
to growing follicles
• Faster frequencies of GnRH, seen just before the midcycle
gonadotropin surge

31. Puberty
• Pubertal reawakening of the reproductive axis
occurs in late childhood and is marked initially
by nighttime elevations in gonadotropin and
gonadal steroid hormone levels
• Both decrease in trans-synaptic inhibition to
the GnRH neuronal system and an increase in
stimulatory input to GnRH neurons

32. Puberty physiology

35. Low GnRH pulsatility
• Delayed puberty
• Hypothalamic amenorrhea
• Hypogonadotrophic Hypogonadism
• Hyperprolactinemia
• Obesity-related hypogonadism

36. High GnRH pulsatility
• PCOS
• Precocious Puberty

37. GnRH agonist
• Suppression of spontaneous ovulation as part
of controlled ovarian hyper-stimulation
• Anti-androgenic therapy in Prostate CA
• Precocious puberty
• Estrogen dependant condition- Menorrhagia,
Endometriosis, Adenomyosis
• Gender Dysphoria

38. GH physiology
• Diurnal rhythm with approximately two-thirds of the total daily GH
secretion produced at night triggered by the onset of slow-wave
sleep
• Major GH secretary pulses accounting for up to 70% of total daily
secretions
• Decline in GH status with aging occurs by a change in pulse
amplitude rather than frequency &vise-versa
• Both sexes have an increased pulse frequency during the nighttime
hours, but the fraction of total daily GH secretion associated with
the nocturnal pulses is much greater in men
• Women have more continuous GH secretion

40. Features
• Daily GH secretion rate varies over two orders
of magnitude from a maximum of nearly 2.0
mg/day in late puberty to a minimum of 20
μg/day in older or obese adults
• Neonatal period is characterized by markedly
amplified GH secretary bursts followed by a
pre-pubertal decade of stable, moderate GH
secretion of 200 to 600 μg/day

42. ACTH/Glucocorticoids
• Locus of ACTH pulse generation- parvocellular CRH and/or arginine-
vasopressin (AVP) neurons in the paraventricular nuclei driven by
ACTH
• Follows a high frequency of pulses, with amplitude being the
primary variation in its release
• Within the circadian cycle approximately 15 to 18 pulses of ACTH
can be discerned, their height varying with the time of day
• Regular pulses of glucocorticoids, mainly cortisol released in
a circadian pattern in addition to their release as a part of the stress
response

43. Prolactin Pulsatility
• Discrete pulses superimposed on basal
secretion and exhibits a diurnal rhythm with
peak values in the early morning hours

44. TSH pulsatility
• Circadian periodicity, with a maximum
between 9 pm and 5 am and a minimum
between 4 pm and 7 pm
• Smaller ultra-radian TSH peaks occur every 90
to 180 minutes

45. Insulin Oscillation
• Driven by oscillation of the calcium concentration
in the cells
• Accomplished by intra-pancreatic neurons and do
not require neural input from the brain
• ATP/NO involved
• The effect of these neural factors is to induce
sudden dramatic elevation of calcium in the
cytoplasm by releasing calcium from the
endoplasmic reticulum (ER) of the beta cells

47. PTH pulsatility
• Recur every 8.5 (range 5–12) min and
constitute about 50% of total PTH secretion in
the normal human
• Clinical application of this insight is once-daily
administration of biosynthetic N-terminal PTH
(1–34) for the treatment of osteoporosis

48. Pulsatility measurement &
challenges

49. Effect of dilution in sampling volume
• The nominal time delay for blood-borne
hormones to move from the site of secretion
to the point of sampling would be less than
the circulation time
• This time latency (30 sec) is relatively
insignificant analytically compared with
nominal sampling intervals of 5–20 min and
typical hormone half-lives of 5–300 min

50. Influences of basal secretion/half life
• For any given pulse number, shape, size, and
variability, increasing basal (nonpulsatile)
secretion or hormone half-life elevates mean and
inter-peak hormone concentrations linearly
• Higher interpulse concentrations in turn
attenuate the signal-to-noise ratio, if the pulse-
detection methodology depends upon the
fractional (percentage) increment of the peak

51. • Illustrated by comparing 10-min sampled 48-h LH and
FSH concentration profiles, for which approximate
slow-phase half-lives are 1.5 and 10.2 h respectively
• Percentages of basal secretion are 10 and 50%
respectively
• The longer half-life and higher basal secretion rate of
FSH than LH together elevate inter-pulse
concentrations
• Discriminating pulsatile secretion is more difficult for
FSH than for LH

52. Sampling near the site of anatomic
secretion
• Systemic Testo pulses are difficult to discern,
but direct catheterization of the internal
spermatic vein in men can
• Individual Te pulses so identified coincide with
LH pulses generated 40 min earlier
• Analogously, sampling in the portal vein for
Insulin

53. Altered Pulsatility in
pathophysiology

54. Neuro-Endocrine Neoplasia
• High interpulse hormone concentrations or
increased basal secretion rates
• Relative secretary autonomy
• Expression of feedback activated receptors
deficient
• Disruption of the orderly secreted patterns
• Decreased serial orderliness, regularity, or
reproducibility of hormone-concentration profiles
quantified by the approximate entropy (ApEn)
statistic
• Frequent but diminutive secretory bursts

55. T2DM
• Diminished secretary-burst mass (as evaluated
by deconvolution analysis)
• Decreased secretary pattern orderliness (as
assessed by ApEn, a regularity measure)

56. Hyperprolactinemia vs Prolactinoma
• Tumoral prolactin secretion is marked by more
frequent peaks than benign
Hyperprolactinemia
• The basis for apparently increased pulse
number is not clear, but might reflect bursts of
prolactin released by clusters of autonomous
tumor cells

57. Primary Hyperparathyroidism
• Normal pulse frequency with irregular
patterns superimposed upon high basal
concentrations

58. Analysis of Pulsatility

59. Deconvolution analysis
• Steps-
 quantify the mass of hormone secreted in pulses and
basally
 estimate the amount removed
 allow for unexplained biological variability
• Main Components:
 Half-life of hormonal elimination
 Basal Secretion rate
 Secretory-burst size (amplitude or mass) and shape
(waveform)
 Number and locations of secretory bursts

61. Analysis of Multi-hormone (Ensample)
analysis
• Prototypical signal pair comprises PTH and Ca2
• Analytical models must account for three features of
biological systems
 reciprocal interactions, which evolve either
concurrently (in parallel) or after time delays (in series)
 nonlinearities at points of signal convergence (e.g.,
inhibitory and stimulatory dose-response interfaces)
 unknown random (stochastic) variability due to
procedural (e.g., assays) and biological factors (e.g.,
pulsing mechanisms)

62. Examples
• Estimate endogenous feed-forward dose-
response functions linking concentrations of
ACTH and LH with secretion rates of cortisol
and Te respectively in healthy adults

64. Approximate entropy (ApEn) as an
ensemble measure
• Correlates with subclinical changes often undetected
by more classical time-series means
• Predictive of subsequent clinical changes and per-
subject longitudinal evolution, such as pubertal
development, physiological aging, and postsurgical
hormonal recovery
• Subtle differences in instances in which no clear waves
or pulses are easily identifiable
• Calculated as an absolute value or as a z score

66. Take Home Message
• Pulsatility in endocrinology spectrum covers
from Hypothalamo-pituitary axis to pancreas
& parathyroid
• GnRH & GH –prime examples
• Understanding pulsatility in GnRH holds the
key to treat & diagnosed gonadal disorders
• Need to understand the various analyzing
methods to know the pulsatility of hormones

67. Thank you…………….