Direct visualization of rat peritubular myoid cell contraction in response to endothelin

Seminiferous tubule contractility is fundamental for sperm progression towards the rete testis; hence its regulation represents a key point in male fertility. Endothelin-1 (ET-1), a potent stimulator of smooth muscle contractility, has recently been shown to be produced in the testis, as well as to bind to specific receptors on myoid cells and thereby activate intracellular signaling. The present paper illustrates contraction of isolated myoid cells in response to ET-1 both in phase-contrast and scanning electron microscopy. Moreover, a simple method is described that allows visualization of a dramatic endothelin-induced rearrangement of myoid cell actin filaments in whole-mount preparations of seminiferous tubules. The response, which can be observed within seconds from stimulation, was paralleled by cell shape changes that were well apparent in scanning electron microscopy. The present report provides the first direct evidence that endothelin is an agonist of myoid cell contractility. Moreover, the experimental approach described could represent a promising tool for the screening of potential agonists of peritubular contractility and for the analysis of their mechanisms of action. In this regard, preliminary evidence is presented on myoid cell contractile response to [Arg8]-vasopressin.