Mark A. Nelson

INTRACEREBROVENTRICULAR INFUSIONS OF CORTICOTROPHIN RELEASING FACTOR (CRF) AND ACTH RAISE BLOOD PRESSURE IN SHEEP

1. Infusion of synthetic ovine CRF (10 or 100 μg/h) into the lateral cerebral ventricle for 24 h increased mean arterial blood pressure of conscious sheep.

Metabolic and Blood Pressure Effects of 6α-Methylprednisolone in the Conscious Sheep

Methylprednlsolone has been reported to be produce hypertension in the rat but to have no effect on blood pressure in the dog. In this study, methylprednlsolone infused to conscious sheep for up to 10 days at either 20 μg/kg/hr or 100 μg/kg/hr, failed to induce a hypertensive response. Metabolic effects characteristic of glucocorticoid activity, such as increased water intake and urine volume, were observed in all animals. No consistent decrease in plasma potassium concentration was observed with either rate of infusion, indicating a lack of in-vivo mlneralocortlcoid activity. In the conscious sheep, like the dog, methylprednlsolone exhibits only glucocorticoid activity and does not increase blood pressure.

Serotonergic mechanisms and blood pressure in sheep.

This study examined the effects of the serotonergic (5-HT2) antagonist ketanserin in sheep on haemodynamic responses to infused serotonin (5-HT), development of adrenocorticotrophin (ACTH)-induced hypertension, and the effect of ACTH on in vivo pressor responsiveness to 5-HT. Serotonin produced a dose-related increase in mean arterial pressure and heart rate. These increases in mean arterial pressure were attenuated or abolished by ketanserin, but increases in heart rate were enhanced. Ketanserin modified the pressure response to the alpha-adrenergic agonist phenylephrine, and did not further lower mean arterial pressure in sheep pretreated with the alpha-antagonist prazosin. Thus, ketanserin exhibits alpha-adrenergic antagonism in sheep. Ketanserin infusion lowered mean arterial pressure in normal sheep but did not affect the pressor response to ACTH infusion. There was no difference in pressor responsiveness to 5-HT (0.1-30 micrograms/kg) before and after ACTH treatment. Thus, 5-HT raises mean arterial pressure in sheep in a dose-related fashion, but there is no evidence of a role for 5-HT in ACTH-induced hypertension.

RITANSERIN AND SEROTONERGIC MECHANISMS IN BLOOD PRESSURE AND FLUID REGULATION IN SHEEP

1. In previous studies, exogenous serotonin (5‐HT), administered intravenously, caused dose‐related increases in mean arterial pressure and heart rate in conscious sheep. The 5‐HT2 antagonist ketanserin (0.1 mg/kg per h, i.v.) was shown to lower blood pressure in the conscious sheep primarily through antagonism of α‐adrenoceptors.

KETANSERIN DOES NOT PREVENT ACTH‐INDUCED HYPERTENSION IN SHEEP

1. The role of serotonin (5HT) in the pathogenesis of ACTH‐induced hypertension in sheep has been examined.

THE EFFECT OF THE 'HYPERTENSINOGENIC STEROID, 9α-FLUORO-CORTISOL ON BLOOD PRESSURE IN SHEEP WITH ACTH-INDUCED HYPERTENSION

1. The effect of treatment with 9α‐fluorocortisol (9aFF), a steroid which causes hypertension in sheep, was examined in sheep with ACTH‐induced hypertension.