METABOLIC STUDIES ON THE RABBIT CORPUS CAVERNOSUM

Erectile function (erection and detumescence) involves the complex int eraction of direct neuronal stimulation of corporal smooth muscle, neu rohumoral release of specific endothelial contractile and relaxant fac tors, and secondary modulation by a variety of putative neuropeptides and vasoactive modulators. The net result is a rapid and sustained rel axation of the smooth muscle elements during erection and contraction of the smooth muscle during detumescence. Proper function of the corpo ral tissue is dependent upon cellular metabolism of glucose and the ge neration of cellular energy in the form of high energy phosphates. The current study characterizes the following metabolic parameters of the rabbit corpus cavernosum: Tissue concentrations of creatine phosphate (CP), ATP, ADP, and AMP; maximal rate of glucose metabolism to lactic acid and CO2; and activities of the enzymes creatine kinase (CK), cit rate synthase, and malate dehydrogenase. For comparative purposes only , bladder smooth muscle preparations were analyzed simultaneously with and under the same conditions as the corpus cavernosum. The results a re as follows: The concentrations of ATP and CP in the corpora were si gnificantly lower than the concentrations in bladder. In the corpora, the tissue concentration of CP was lower than the tissue concentration of ATP, whereas the concentration of CP in the bladder was higher tha n the concentration of ATP. The rate of glucose metabolism to lactic a cid and to carbon dioxide was similar for both bladder smooth muscle a nd corpus cavernosum. The maximal enzymatic activity of the mitochondr ial enzyme citrate synthase was similar for both tissues; similarly, t here was no significant difference in the activity of malate dehydroge nase between the two tissues. However, the CK activity of the bladder smooth muscle was significantly greater than the activity in the corpu s cavernosum. One important factor that must be considered is that onl y 34% of the corpus cavernosum is smooth muscle, the balance being ext racellular matrix, endothelium, and cytoskeletal elements. Thus, the d ifferences between these two tissues may well be related to the differ ent structural components.