Differential actions of gonadotropin-releasing hormone and human chorionicgonadotropin on interstitial fluid volume and immunoglobulin G concentrations in adult rat testis

Gonadotropin-releasing hormone (GnRH) agonists regulate testicular intersti tial fluid (tIF) volume, most probably via specific receptors on Leydig cel ls. The aim of this study was to confirm the interaction between GnRH and L eydig cells in regulation of testicular fluid, and to examine the effects o n serum proteins in testis. Unilateral intratesticular injection of a GnRH agonist (100 ng/ testis) caused a 50% reduction in tIF volume within 2 hour s. Destruction of Leydig cells by treatment with ethane dimethane sulfonate also caused a similar decline in tIF volume; however, GnRH agonist treatme nt had no additional influence on this response in Leydig cell-depleted tes tes. GnRH agonist treatment had no effect on serum protein permeability in testis as indicated by maintenance of the tIF/serum immunoglobulin G (IgG) concentration gradient. Injection of human chorionic gonadotropin (hCG, 100 IU) had no effect on tIF volume at 2 hours, but increased the permeability of the testicular vasculature to serum IgG. At 20 hours after hCG injectio n, tIF volume was increased twofold, while the testicular permeability barr ier to IgG appeared to have been restored. These data indicate that the acu te inhibitory action of GnRH on vascular fluid permeability is dependent up on Leydig cells, confirming that these cells are the primary site of GnRH a ction on testicular vasculature. The data also indicate that supraphysiolog ical doses of hCG cause a rapid increase in testicular permeability to seru m proteins, which occurs prior to the well-characterized stimulation of tIF volume. These data provide further evidence that the concentration of seru m proteins in tIF and the volume of tIF are both under regulatory control i nvolving Leydig cells, but are independently regulated.