The Effect of Progesterone on Coronary Blood Flow in Anaesthetized Pigs

Abstract

The present study was designed to investigate the effect of progesterone on the coronary circulation and to determine the mechanisms involved. In pigs anaesthetized with sodium pentobarbitone, changes in left circumflex or anterior descending coronary blood flow caused by intravenous infusion of progesterone at constant heart rate and arterial blood pressure were assessed using an electromagnetic flowmeter. In 14 pigs, infusion of 1 mg h−1 of progesterone caused an increase in coronary blood flow without affecting left ventricular dP/dtmax (rate of change of left ventricular systolic pressure) and filling pressures of the heart. In a further four pigs, this vasodilatory coronary effect was enhanced by graded increases in the dose of the hormone of between 1, 2 and 3 mg h−1. The mechanisms of the above response were studied in the 14 pigs by repeating the experiment after haemodynamic variables had returned to the control values observed before infusion. In six pigs, blockade of muscarinic cholinoceptors and adrenoceptors with atropine, propranolol and phentolamine did not affect the coronary vasodilatation caused by progesterone. In the remaining eight pigs, this response was abolished by intracoronary injection of Nω‐nitro‐L‐arginine methyl ester (L‐NAME) even when performed after reversing the increase in arterial blood pressure and coronary vascular resistance caused by L‐NAME with continuous intravenous infusion of papaverine. The present study showed that intravenous infusion of progesterone primarily caused coronary vasodilatation. The mechanism of this response was shown to involve the endothelial release of nitric oxide.

Human Placental Lactogen Decreases Regional Blood Flow in Anesthetized Pigs

“…Previous reports in anesthetized pigs have shown that 17β-estradiol and progesterone cause vasodilatation through mechanisms which involve the endothelial release of nitric oxide [27, 33, 34]. The increase in the maternal peripheral serum levels of human placental lactogen which accompanies the spontaneous increases in maternal peripheral serum levels of estrogens and progesterone as pregnancy advances [see, for example, ref.…”

Effect of Progesterone on Peripheral Blood Flow in Prepubertal Female Anesthetized Pigs

“…The infusions were completed in 1 h by using an infusion pump (Model 22, Harvard Apparatus) working at constant rate of 1 ml/min. In a previous study on the effects of progesterone on the coronary circulation, it has been shown that this period of 1 h was required to attain steady state changes in coronary blood flow [1]. After the infusion was stopped, observations were continued for 1.5 h. The dose of progesterone used corresponded to the hourly amount of hormone which is reported to be produced by the corpus luteum during the mid-luteal phase of the ovarian cycle in women [11]and is reported to be analogous in pigs [12].…”

“…The present investigation was therefore designed, in a similar manner of that of Molinari et al [1], to quantify the effect of acute administration of progesterone on mesenteric, renal and iliac blood flow in anesthetized female pigs and to determine the mechanisms involved. For this purpose, experiments were performed during constant heart rate and arterial blood pressure to avoid interference by hemodynamic and reflex effects.…”

“…For instance, we have recently shown that intravenous infusion of progesterone in anesthetized pigs primarily caused coronary vasodilatation which involved the release of nitric oxide [1]. Others have shown that vaginal implants of progesterone in non-pregnant ovariectomized sheep increased nitric oxide synthase expression in the endothelium of the uterine artery but not in that of the omental, renal or mammary arteries [2], and that progesterone relaxes pre-contracted segments of small saphenous artery of the rat [3].…”

Ovarian Hormones During Different Phases of Ovarian Cycle In Healthy Young Women

“…Some investigators suggested that progesterone in high concentration potentiate the GABA mediated baroreflex sympatho-inhibition within RVLM 9,10 . Again, some investigators have suggested that progesterone may cause vasodilatation by releasing NO from endothelium 18,19 .…”