ABSTRACT
The effect of PGE^, P5P?a and PGI0 on tilu lion induced by different mechanisms was studied in the isolated rat mesenteric arteiy as described by McGregor (1965)
Vasoconstriction was induced by mechanisms involving dii modes of calcium utilization viz: (i) Pharmaccnechanical pathway by low doses of the adrenergic neurotransm.itter, noradrenaline acting at - receptor; (ii) electromechanical pathway by 1.1 b potassium-and” (iip.) agents which facilitate Ca influx e.g.
A23187. !
The prostaglandins potentiated the vasoconstrictor effect
of NA. Potentiation factors calculated from different doses
of the prostaglandins showed the effects of the prostaglandins
to be dose - dependent and FGE^ to be significantly more potent
(P>0.005) than PGE,,a and PGI^* The prostaglandins failed to
potentiate high potassium - induced vasoconstriction. PChi^ also
failed to potentiate NA if the vasoconstrictor effects were
evoked in Ca~ - free Krebs solution; but the degree -of potentia
2+
tion increased with increase in the concentration of Ca ions in the perfusion fluid. This result suggested strongly that the
potentiation was associated with external calcium. Evidence is presented to show that potentiation was not prejunctional since
cocaine, bretylium and reserpine pretreatment did not materially alter the effect of It was concluded that prostaglandins
potentiated HA vasoconstriction by facilitating Ca influx.
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The mechanism 'of this facilitation is discussed.
ITA vasoconstriction was competitively antagonised by adrenoceptor antagonists-phentolamine, tolazoline, yohimt• and phenoxybenzamine (in low concentrations). The blockade caused by these antagonists was reversed by PGE?. By comparing NA dose-ratios in the presence of antagonist with dose-ratios in
the nresence of antagonists plus different doses of PGB0, I
^
showed 1hat the degree of reversal was related to the dose of PGE. For example, the NA dose - ratio for yohimbine (1.28 x ICT^I)
o
was reduced from 26.6 + 0.9 to ^.7 + 0.1 when PGE^ (2.8 x 10 M)
was included in the perfusion fluid with the antagonist. The
reveio_< of antagonism was not due to a change in the binding
characteristics of the aj- adrenoceptor since pA^ values for the
antagonist were not significantly different (P^.0.05) when PGS was
included with the antagonists. Evidence is presented which suggests
that reversal of antagonism involved utilization of internally
bound calcium since reversal of antagonism occured even after 2+
the omission of Ca from the external medium. In this sense, the mechanism of reversal was different from that of potentiation. Furthermore, the degree of reversal (measured as-reversal factor) was quantitatively greater than would be the nans- if reversal was simply a reflection of the enhgresponsiveness of the vascular
muscle to NA.
iii -
In contrast to the "competitive” - adrenoceptor antagonists, did not reverse the block of ITA vasoconstriction
caused by phenoxybenzanine (high doses); verapamil, cinnarizine or prazosin. All these agents caused blockade of NA that was not competitive in'nature. Since noneof the competitive
CKE, A (2021). Interaction Of Prostaglandin E (Pge ) With Noradrenaline And Its Antagonists In The Isolated Mesenteric Artery Oe Rat. Afribary. Retrieved from https://tracking.afribary.com/works/interaction-of-prostaglandin-e-pge-with-noradrenaline-and-its-antagonists-in-the-isolated-mesenteric-artery-oe-rat
CKE, AYOTUNDE "Interaction Of Prostaglandin E (Pge ) With Noradrenaline And Its Antagonists In The Isolated Mesenteric Artery Oe Rat" Afribary. Afribary, 21 Apr. 2021, https://tracking.afribary.com/works/interaction-of-prostaglandin-e-pge-with-noradrenaline-and-its-antagonists-in-the-isolated-mesenteric-artery-oe-rat. Accessed 06 Nov. 2024.
CKE, AYOTUNDE . "Interaction Of Prostaglandin E (Pge ) With Noradrenaline And Its Antagonists In The Isolated Mesenteric Artery Oe Rat". Afribary, Afribary, 21 Apr. 2021. Web. 06 Nov. 2024. < https://tracking.afribary.com/works/interaction-of-prostaglandin-e-pge-with-noradrenaline-and-its-antagonists-in-the-isolated-mesenteric-artery-oe-rat >.
CKE, AYOTUNDE . "Interaction Of Prostaglandin E (Pge ) With Noradrenaline And Its Antagonists In The Isolated Mesenteric Artery Oe Rat" Afribary (2021). Accessed November 06, 2024. https://tracking.afribary.com/works/interaction-of-prostaglandin-e-pge-with-noradrenaline-and-its-antagonists-in-the-isolated-mesenteric-artery-oe-rat