Peripheral progesterone concentrations in the luteal-phase ewe: effects of a beta-adrenergic receptor antagonist and...

Peripheral blood samples were collected at 10-min intervals from three conscious sheep in which ovulation had been induced 6-10 days previously using exogenous hormones. Saline was infused into a jugular vein for about 1 h, followed by the experimental drug for 1-2 h and followed by saline again for a further 2 h. The experiments were repeated following induced luteolysis and ovulation. The infusion of a beta-adrenergic antagonist (propranolol) into three conscious luteal-phase ewes decreased (P less than 0.05) the peripheral progesterone concentration in each animal. Infusions of beta 2-adrenergic agonists (ritodrine and salbutamol) increased (P less than 0.05) the progesterone concentration in four out of eight experiments. The beta-adrenergic antagonist decreased the heart rate and the beta 2-adrenergic agonist increased it; the arterial blood pressure and respiratory rate were unaffected. The decrease in the progesterone concentration in response to the beta-adrenergic antagonist suggests that the normal ovarian secretion of progesterone is partly the result of sympathetic stimulation, and that the sympathetic innervation of the ovary may have a physiological role in modulating progesterone secretion.