Sucrose drinking reduces dorsal hypothalamic β-endorphin levels in spontaneously hypertensive rats but not in Wistar-Kyoto rats

Abstract

The present study was performed to test whether drinking of a 10% sucrose solution would preferentially alter tissue content of β-endorphin in dorsal and ventral hypothalamic fragments from the spontaneously hypertensive rat (SHR), as opposed to the Wistar-Kyoto rat (WKY). Changes were correlated with cardiovascular function and circulating catecholamine levels to asses the role of hypothalamic β-endorphin, a putative mediator of sucrose-induced changes in cardiovascular sympathetic nervous tone. Male rats were trained to consume their total 24-h water intake in a single period between 0900–1100 h. Catheters were chronically implanted to sample blood and to record arterial blood pressure and heart rate. The experimental protocol consisted of a recording session, which included a 10-min drinking period wherein rats consumed 8 ml of either sucrose solution or deionized water. Rats were sacrificed and hypothalami removed for analysis of β-endorphin content. Comparable increases in blood pressure were noted in SHR and WKY during drinking of either sucrose or water. Drinking-induced tachycardia was blunted in SHR drinking sucrose. Plasma norepinephrine was increased only in sucrose-drinking SHR. Plasma glucose levels were elevated in both SHR and WKY following drinking of sucrose, but not water. β-Endorphin levels were reduced ( p < 0.05) in dorsal, but not ventral, hypothalamic fragments only in SHR drinking sucrose. The sucrose-induced changes in β-endorphin did not correlate with blood pressure responses. The results indicate an exaggerated stimulation of β-endorphin release in the dorsal hypothalamus following sucrose ingestion in SHR.