Mechanism of noradrenaline influence on the secretion of ovarian oxytocin and progesterone in conscious cattle.

Noradrenaline stimulates the concomitant release of ovarian oxytocin and progesterone in cattle within a few minutes, but the mechanism of its action is unknown. Changes in alpha- and beta-receptors and blood pressure were considered as possible mechanisms of the noradrenaline effect. Heifers in group 1 (n = 4) were infused with noradrenaline (0.16 microgram kg-1 min-1) for 30 min into the aorta abdominalis (cranial to the origin of the ovarian artery) on day 10. On days 11 and 12 before noradrenaline, phentolamine (alpha-blocker; 30 micrograms kg-1 min-1) or propranolol (beta-blocker; 5 micrograms kg-1 min-1) were infused for 30 min. Four other heifers were infused with noradrenaline only as controls. Only propranolol inhibited the stimulatory effect of noradrenaline on the secretion of progesterone and oxytocin. In group 2, heifers (n = 4) were infused, making use of the latin square design, with vasoconstrictive (angiotensin; 0.042 microgram kg-1 min-1) or vasodilatory (xanthinol-theophylline nicotinate; 250 micrograms kg-1 min-1) drugs that do not act through the adrenoceptors. Noradrenaline (0.3 microgram kg-1 min-1) was given 1 h later as in group 1. Blood pressure changes were measured in the posterior aorta abdominalis and oxytocin and progesterone concentrations were determined in the blood samples collected from the jugular vein. Noradrenaline and angiotensin increased (P < 0.01), whereas xanthinol decreased (P < 0.01), blood pressure during their infusion. However, the rise of oxytocin and progesterone concentrations was observed only after noradrenaline infusion.(ABSTRACT TRUNCATED AT 250 WORDS)