Reduction of blood flow in the adenohypophysis of rats by bromocriptine

The possibility that bromocriptine has a selective effect on blood flow in the adenohypophysis was examined in rats. Twenty-four anesthetized male Wistar rats underwent measurement of blood flow using the hydrogen clearance method. Intravenous injection of 50 micrograms/kg bromocriptine reduced the blood flow in both the medial and lateral parts of the adenohypophysis to about 70% of the baseline value. Simultaneously measured cerebral cortical and white matter flows were unchanged. Similar results were obtained following administration of a higher dose (500 micrograms/kg) of bromocriptine. This phenomenon cannot be attributed to the decrease in blood pressure. The course of change in blood flow in the medial and lateral adenohypophysis did not follow that of the mean arterial blood pressure, and the alteration of blood pressure remained within the limits of autoregulation in the adenohypophysis. The results indicate that bromocriptine is capable of reducing blood flow selectively in the pituitary region. This mechanism may contribute to the clinical usefulness of this drug.