Effect of drugs on arterial blood pressure of cat

1. EFFECT OF DRUGS
ON ARTERIAL BLOOD
PRESSURE OF
ANAESTHETIZED CAT

2. STEPS
1 – Animal : Cat.
2 – Anesthesia : Induction by inhalation of diethylether then
maintenance by I.V. chloralose.
3 – Dissection : exposure of :
a – Trachea for endotracheal intubation to allow for
artificial respiration.
b – Carotid artery for recording arterial blood pressure.
c – Femoral vein for injection (infusion) of tested drug
(via saline).

3. LIST 0F ABBREVIATIONS
 C.O. = Cardiac output
 S.D. = Small dose
 L.D. = Large dose
 D.B.P = Diastolic blood pressure
 S.B.P. = Systolic blood pressure
 T.P.R. = Total peripheral resistance
 V.C. = Vasoconstriction.
 V.D. = Vasodilatation

4. IMPORTANT STATEMENTS ABOUT ARTERIAL
BLOOD PRESSURE
1- S.B.P. Is controlled by both C.O. and T.P.R.
2 - D.B.P. Is controlled mainly by T.P.R.

5. 3 - Activation of β1 – adrenoceptors
cardiac stimulation increases C.O.
elevates S.B.P. mainly.
4 – Activation of β2 – adrenoceptors
V.D. Decreases T.P.R
Lowers both S.B.P and D.B.P.
5 - Activation of α1 – adrenoceptors
V.C. increases T.P.R
Elevates both S.B.P. and D.B.P

6. 6 – Activation of M - cholinoceptors
both cardiac inhibition and V.D.
Decrease both C.O. and T.P.R
lowers both S.B.P and D.B.P

7. 7 – Activation of Nn - cholinoceptors of both
sympathetic ganglia and adrenal medulla
release of endogenous
catecholamines activation of both α
and β adrenoceptors increases both
T.P.R. and C.O. Elevates both S.B.P.
and D.B.P.
N.B : Nicotine S.D. activates directly Nn and
indirectly α and β receptors

8. 8 – Angiotensin ӀӀ V.C. Increases
T.P.R. Elevates both S.B.P and
D.B.P.
9 - Vasopressin V.C. Increases
T.P.R. Elevates both S.B.P and
D.B.P.
10 – Histamine activates both H1 (mainly) and H2
receptors V.D. Decreases
T.P.R. Lower both S.B.P and D.B.P.

9. N.B.
 Acetylcholine S.D. acts on muscarinic
receptors only.
 Acetylcholine L.D. acts on muscarinic and
nicotinic receptors.
 Atropine acts as a competitive blocker of all
muscarinic receptors.
 Epinephrine acts on α1, α2, β1, β2.
 Phentolamine acts as a non-selective α-
adrenoceptor blocker.

10. EXPERIMENT
 1- Acetylcholine S.D. produces hypotension.
 2-Injection of atropine, it does not change the blood
pressure.
 3-Re-injection of acetylcholine S.D. after atropine it
does not change the blood pressure.
 4-Injection of acetylcholine L.D. after atropine
produces hypertension. (acetylcholine reversal)
 5- Injection of epinephrine produces hypertension.
 6-Injection of phentolamine produces hypotension.
 7-Re-injection of epinephrine after phentolamine
produces hypotension. (epinephrine reversal)

11. DETERMINATION OF THE
SITE OF ACTION OF AN
UNKNOWN DRUG
AFFECTING BLOOD
PRESSURE
OF ANAESTHETIZED CAT

12. HYPOTENSIVE UNKNOWN
1- Muscarinic receptors only : e.g. Bethanechol
* The hypotensive effect of drugs acting on
muscarinic receptors only could be abolished
completely by atropine.
2 – Muscarinic & Nicotinic receptors
e.g. Acetylcholine,Carbachol
* The hypotensive effect of these drugs is
reversed by atropine.

13. 3 - β2 – receptors e.g. Isoprenaline
* The hypotensive effect of these drugs is : -
a – Not anatagonised by atropine.
b – Abolished by non-selective β blockers
e.g. propranolol.

14. 4 – Histamine (H1 & H2) receptors : -
* The hypotensive effect of histamine is : -
a – Not anagonised by atropine or
propranolol.
b – Abolished by combination of
H1 blocker (e.g. Mepyramine)
+ H2 blocker (e.g. Cimetidine).

15. 5 – Direct effect on vascular smooth muscle
e.g. Hydralazine , Calcium channel
blocke , Nitrites & Nitrates.
* The hypotensive effect of these drugs is
NOT anatagonized by atropine or
Propranolol or combined H1 + H2
blockers

16. HYPERTENSIVE UNKNOWN
1 – Nicotinic receptors in ganglia and
adrenal medulla e.g. : Nicotine small dose
* the hypertensive effect of these drugs is :-
a – Blocked by ganglion blockers
(e.g. Mecamylamine)
b – Reversed by alpha – blockers
(e.g. Phentolamine)

17. 2 – α & β – adrenoceptors e.g. Epinephrine.
* the hypertensive effect of these drugs is : -
a – Not abolished by ganglion blockers
(e.g. Mecamylamine).
b – Reversed by alpha-blockers
(e.g. Phentolamine).

18. 3 – α-adrenoceptors e.g. Norepinephrine (α + β1) &
Phenylephrine (α1 only).
* The hypertensive effect of these drugs is :-
a – Not blocked by ganglion blockers
(e.g. Mecamylamine).
b - Abolished by alpha-blockers e.g
Phentolamine & Phenoxybenzamine.

19. 4 – Angiotensin ӀӀ receptors
* The hypertensive effect of these drugs is :-
a – Not blocked by ganglion blockers
(e.g. Mecamylamine) or alpha-blockers
(e.g. Phentolamine).
b – Abolished by Saralasin (Angiotensin ӀӀ
receptors blockers).

20. 5 – Vasopressin receptors
* The hypertensive effect of vasopressin is
NOT anatagonized by ganglion blockers
(e.g. Mecamylamine) or α blockers
(e.g. phentolamine ) or Saralasin.