Contractility of rat gubernacula affected by calcitonin gene-related peptide and β-agonist

Abstract

Purpose The effects of calcitonin gene-related peptide (CGRP), isoprenaline, and guanethidine on the neonatal rat gubernaculum were investigated in organ culture with the aim of seeing whether β-agonists or β-antagonists are involved in gubernacular development during testicular descent. Methods A total of 200 gubernacula were studied. The gubernacula (n = 20 for each experiment) from male rat pups were incubated in aerated culture medium with isoprenaline (1 and 10 μmol/L) with/without CGRP (714 nmol/L) or guanethidine (1 and 10 μmol/L) with/without CGRP (714 nmol/L). Cultures were observed for 5 days by video camera to see spontaneous rhythmic contractions, which are known to correlate with normal gubernacular migration in the rodent. Results Of gubernacula cultured without CGRP, 60% showed contractions by day 5, and the groups of isoprenaline and 10 μmol/L guanethidine showed similar rates, but only 15% of the 1 μmol/L guanethidine group showed contractility ( P < .005). In contrast, of the gubernacula cultured with CGRP, each group showed high contractility from day 2 of the culture, and there was no difference between each group and the CGRP-alone group. Conclusions Although the β-blocker showed a weak inhibitory effect on de novo gubernacular contractility, CGRP had a stronger effect on contractility, overriding any possible effects of the β-neuron pathway. The contractility of the rat gubernaculum during testicular descent is primarily mediated by the genitofemoral sensory nerve fibers via release of CGRP, but β-adrenergic nerves also may be involved.