Abstract
Ovariectomy was performed at 4 weeks of age (W), and the rats were used when they were 33 and 75 W old. Systolic blood pressure (BP) was measured by the tail-cuff method. Naloxone (10 mg/kg) was given i.p. Catecholamines (CA) were determined with HPLC. Norepinephrine (NE) was not significantly altered in intact rats by naloxone; however, a significant increase in NE appeared in the plasma, hippocampus, thalamus plus mid-brain and hypothalamus in castrated rats following naloxone. With naloxone treatment, dopamine (DA) was significantly increased in the plasma and hypothalamus, but decreased in the cerebral cortex in intact rats; and with castrated rats, there was a tendency to see an increase in plasma DA and significantly increased levels of DA in the thalamus plus mid-brain and hypothalamus. This suggests that in female brain, lack of estrogen in the castrated rats leads to an increase in intrinsic opiate, and this in turn inhibits CA release. On the other hand, when naloxone was administered to castrated rats, intrinsic opiate was blocked, and, consequently, inhibition of CA release was lost and induction of CA release was enhanced.
