Properties of alpha-1-adrenergic receptors in the rat prostate: Effect of experimental diabetes

We studied the effects of 8 weeks of streptozotocin (STZ)-induced diabetes on the density and the pharmacological properties of alpha(1)-adrenoceptors in the rat prostate using receptor-binding experiments with [I-125]iodo-2[ beta-(4-hydroxyphenyl)-ethylaminomethyl]tetralone [I-125]HEAT. Saturation e xperiments showed the presence of specific [I-125]HEAT-binding sites in the control and diabetic rat prostate and that the induction of diabetes signi ficantly decreased the density of [I-125]HEAT-binding sites in the rat pros tate. [I-125]HEAT-binding sites in the prostate of both groups were inhibit ed by prazosin (nonselective), spiperone (alpha(1B)-selective), WB4101 and 5-methylurapidil (alpha(1A)-selective) and BMY7378 (alpha(1D)-selective) wi th the following rank order of K-i values: prazosin < WB4101 < 5-methylurap idil < spiperone < BMY7378, indicating a similar pharmacological profile of alpha(1)-adrenoceptor in the 2 groups. Comparing the K-i values of the rat prostate with those obtained from the r at submaxillary gland (alpha(1A)), rat spleen (alpha(1B)), rat vas deferens (alpha(1A) + alpha(1B)) and those reported for cloned alpha(1D), indicates the predominance of the alpha(1A) + alpha(1B) or the alpha(1A) subtype in the rat prostate. The present study demonstrates that STZ-induced diabetes downregulates the expression of alpha(1)-adrenoceptor in the rat prostate, without significantly affecting the receptor subtype specificity.