The effects of β-endorphin (β-END) on cardiovascular and behavioral dynamics in conscious rats

Abstract

β-Endorphin (β-END) a product of the proopiomelanocortin (POMC) has been demonstrated to play a role in the regulation of metabolic and autonomic responses. Recent studies have suggested the involvement of the endogenous opioid system in cardiovascular control. Previous studies conducted in our laboratory using anesthetized animals investigated the actions of β-END and other POMC derived peptides on sympathetic and cardiovascular dynamics. In this study, we determined both the acute and chronic effects of β-END on cardiovascular and behavioral dynamics in conscious unrestrained rats using radio-telemetry. Animals were instrumented with a radio-telemetry transmitter in the abdominal cavity and the attached catheter inserted into the femoral artery for recording of cardiovascular dynamics and activity. They were subsequently implanted with intracerebroventricular (ICV) cannulas. The acute ICV administration of β-END significantly increased the mean arterial pressure (MAP) and heart rate (HR) compared to controls. The cardiovascular responses returned toward control levels after 2h. In contrast, the chronic infusion of β-END significantly decreased the MAP and HR during both the active and inactive phase. Chronic β-END administration also decreased physical activity. Food intake was increased initially and later declined and water consumption followed a similar pattern. We conclude that in the conscious unrestrained animal the acute administration of β-END increases MAP and HR while the chronic infusion of β-END decreases MAP, HR, physical activity, and stimulate a short-term increase in food and water intake.