Patterns of Pituitary Release and Cranial Output of LH and Prolactin in Ovariectomized Ewes

Abstract

Paired blood samples were collected simultaneously from the jugular vein and from the carotid artery of ovariectomized sheep every IS min for several hr each day. All blood samples were assayed for LH and prolactin by radioimmunoassay. Selected samples were also assayed for GH and for total adrenal corticoids. Cranial output (ng/ml) for a pair of samples was denned as the venous concentration (ng/ml) minus the arterial concentration (ng/ml) and was assumed to reflect hormone release by the pituitary and equilibration of circulating hormone with the extravascular spaces of the head. Arterial LH fluctuated widely in ovariectomized ewes showing very regular peaks occurring at about hourly intervals. Cranial output of LH revealed that the pulsatile discharges of LH from the pituitary were both very large and very brief. Venous LH levels were sometimes 3–4–fold greater than arterial levels in the paired sample. Furthermore, it was estimated that these hourly discharges lasted only about 5 min. Arterial levels ...