Naloxone has a local effect on the testis of immature rats

Effect of intratesticular administration of anti-corticotropin-releasing factor antiserum (a-CRF) on testicular function in neonatal rats

The possible physiological role of testicular corticotropin-releasing factor (CRF) in the regulation of testicular functions was studied in neonatal rats. Two microlitres of anti-CRF-antiserum (dilution: 1:10 or 1:100) was injected intratesticularly to 5 d-old rats with two testes and to hemicastrates. Five days after hemicastration and treatment of the remaining testis with the antiserum, serum testosterone concentration and basal testosterone secretion in vitro decreased significantly. Unilateral testicular injection of a-CRF in rats with two testes resulted in a significant drop in serum testosterone level with no change in basal testosterone production. Data indicate that in neonatal rats testicular CRF might be a local stimulator of steroidogenesis.

Local control systems within the testis

A number of physiological and pathological observations cannot readily be explained unless one accepts that there exists within the testis some sort of local control system. This local network of regulatory interactions offers not only an additional level of fine regulation for individual testicular functions, but also creates an opportunity for co-ordination and integration of distinct activities such as germ cell development and androgen production. There is an overwhelming amount of data indicating that the testis produces a variety of regulatory molecules and that many of these agonists have marked effects on the function of testicular cells in vitro. Some of these molecules are identical with or are at least related to known hormonal and humoral agonists. Others are novel and require further characterization. The exact cellular origin of many of these regulatory factors remains unknown. This overview has been limited to regulatory interactions between somatic testicular cells. Particular attention has been paid to communications between the interstitial and the tubular compartment. It should be evident that the nature and the significance of these interactions is only beginning to emerge. The major difficulty remains to distinguish effects that are restricted to the specific and often artificial conditions of in vitro systems from phenomena that are relevant to testicular control in vivo. Further progress in this field will rely on the development of appropriate systems to study local interactions in vivo. Valuable attempts have been made in this direction: vitamin A induced synchronization of spermatogenesis may offer a model to study stage dependent alterations in the interstitial compartment (Morales and Griswold, 1987; Bartlett et al, 1989); destruction of Leydig cells followed by substitution with androgens might clarify the role of non-steroidal Leydig cell mediators on tubular function (Shape et al, 1988). Up to now these approaches have failed to demonstrate an important role for local regulatory interactions. It is obvious that both models are relatively crude, however, and that subtle changes may have been missed under the experimental conditions used. It should be stressed that some of the observed complexities may be inherent to local regulatory networks. In fact, such networks tend to display a certain level of redundancy. It is evident, for example, that a number of locally produced mediators can also reach the testis via the circulation. In this setting the relative contribution of circulating and locally produced factors may vary depending on developmental stages, physiological or pathological conditions. A relative redundancy may exist for distinct locally produced mediators.(ABSTRACT TRUNCATED AT 400 WORDS)

Intratesticular injection of [D-Met2-Pro5]enkephalinamide suppresses testosterone secretion of the testis of immature rat

The possible role of enkephalin in the local control of testicular function was studied in neonatal rats. 5- and 10-day old hemicastrated rats were treated intratesticularly with an enkephalin analog [D-Met2-Pro5]enkephalinamide. In 5-day-old rats local injection of different doses (0.1-0.3 micrograms/testis) of the peptide suppressed basal testosterone secretion in vitro in a dose-dependent manner 2 h posttreatment. Intratesticular administration of naloxone prior to enkephalin treatment prevented the decrease in basal testosterone production induced by the opioid agonist. In 10-day-old animals intratesticular injection of 1.0 and 3.0 micrograms/testis of enkephalinamide reduced serum testosterone concentration and basal testosterone secretion in vitro. Systemic injection of the peptide produced no change in steroidogenesis. These results suggest that enkephalins might be among the intratesticular factors regulating Leydig cell functions.

Immunohistochemical localization of enkephalins in adult rat testis: evidence for a gonadotrophin control

The recent detection of immunoreactive POMC derived peptides in the male reproductive tract raised the possibility that these hormones might regulate reproductive function. In addition, a variety of studies suggested that POMC derived peptides have paracrine effects in the testis. In this present study, after HCG addition to the organ culture medium, Sertoli cells cytoplasma became immunoreactive with the enkephalins antisera.

The effect of neonatal vasectomy on testicular function

The effect of unilateral or bilateral vasectomy on testicular weight and basal testosterone production in vitro was studied in neonatal intact and hemicastrated rats. Five days after right-side vasectomy ipsilateral to vasectomy testicular weight increased, and basal testosterone production decreased. Ten days postvasectomy the changes were opposite, and affected both testes. In hemicastrated animals hemivasectomy did not interfere with compensatory hypertrophy but induced a significant decrease in basal testosterone production. The data of the present study suggest that in neonatal animals intact ductus deferens bundle(s) is also required for the full control of testicular weight and basal testosterone secretion.

Expression of proenkephalin messenger RNA by mouse spermatogenic cells

The presence of proenkephalin mRNA in germ cells purified from adult mouse testis were examined using RNA gel- and dot-blot analyses. Both pachytene spermatocytes and round spermatids were shown to contain concentrations of this transcript that are 2- to 3-fold greater than that found for whole mouse testis, on a per microgram of polyadenylylated RNA basis. The detection of proenkephalin mRNA in purified spermatocytes and spermatids could not be accounted for by contamination by either Leydig or Sertoli cells. No proenkephalin mRNA was detectable in extracts of mature sperm. These data suggest that developing germ cells may be a major site of proenkephalin synthesis in the adult testis and that proenkephalin-derived peptides may function as germ cell-associated hormones or autocrine/paracrine factors.

Immunohistochemical localization of enkephalinlike peptides during testicular development in rats

The distribution of opioid peptides is of interest in the rat testes, because the presence of opiate binding sites strongly supports the hypothesis of paracrine function for these peptidergic factors. Testes of Wistar albino rats between birth and adult stage were examined immunocytochemically for enkephalins, dynorphin, and alpha neoendorphin. The presence of immunoreactive enkephalinlike substances was visualized in both interstitial tissue and seminiferous tubules, but no staining was observed for dynorphin or neoendorphin. In interstitial tissue the material stained in Leydig cells raised after birth, declined at day 12, and increased again between day 22 and day 35 of life. From day 35 till adult stage we observed again a slight decrease of immunostaining. In seminiferous tubules, intense immunostaining was observed in stem spermatogonia until day 7 of life. After this period the presence of immunoreactive enkephalinlike material was detected, mainly in some spermatogonia and peritubular primary spermatocytes. These data suggest a possible implication of enkephalinlike peptides in spermatogonesis.

Expression of preproenkephalin-like mRNA and its peptide products in mammalian testis and ovary

The distribution of preproenkephalin mRNA and proenkephalin-derived peptides have been examined in gonadal tissues from rats, hamsters, and cattle. A preproenkephalin mRNA band was detected in the ovaries of all three species and in hamster testis that is identical in size to the 1450-nucleotide mRNA typically found in tissues that express proenkephalin. Rat testis, on the other hand, expresses at least one preproenkephalin-like mRNA that is substantially greater in size (1900 nucleotides). [Met]enkephalin-containing peptides were also detected in each of the gonadal tissues examined. Although the abundance of preproenkephalin-like mRNA in rat testis was comparable to that in rat brain, the testicular content of proenkephalin-derived [Met]enkephalin sequences was less than 4% of the rat brain content. Together these data suggest that preproenkephalin-like mRNA in rat testis is not efficiently translated, proenkephalin-derived peptides undergo rapid turnover in this tissue, or the mRNA in rat testis has a frameshift resulting in an altered coding sequence.

Identification and possible function of pro-opiomelanocortin-derived peptides in the testis

Using antibodies against peptides derived from different portions of the POMC molecule, immunocytochemical evidence suggests that this precursor and/or the peptides present within it are localized in testicular Leydig cells of at least five species. There is no evidence for the localization of these peptides or their precursor in any other cell type in this organ. Examination of testicular extracts by gel filtration, SDS-PAGE, and RP-HPLC indicate that the testis contains low concentrations of POMC-derived peptides relative to brain. Further analysis indicates that POMC is processed to alpha-MSH and beta-endorphin similar to its processing in intermediate pituitary lobe and brain. The relative mobilities of immunoreactive alpha-MSH and beta-endorphin on RP-HPLC columns indicate that they are in the unacetylated state as in brain and in contrast to the acetylated forms in the intermediate pituitary lobe. The potential for Leydig cells to synthesize POMC and its peptides was suggested by the demonstration of POMC-like mRNA in total testis and Leydig cell cultures. The size of the POMC-like mRNA is approximately 150 base pairs shorter than anterior or intermediate pituitary POMC mRNA. POMC-like mRNA activity has also been localized to Leydig cells in sections of testes using in situ hybridization. Immunostainable beta-endorphin and other POMC-derived peptides are present in testicular Leydig cells during fetal life and following puberty at times when testosterone secretion is maximal. The accumulation of immunostainable POMC-derived peptides in Leydig cells is dramatically increased by LH and hCG. A variety of observations suggests that testicular cells can respond to POMC-derived peptides. ACTH and the MSHs stimulate growth and cAMP accumulation in Sertoli cells. By contrast, studies using antagonists suggested that beta-endorphin and/or another testicular opioid inhibit Sertoli cell proliferation and ABP secretion. These observations are consistent with the postulate that different portions of the POMC molecule may have opposite effects on Sertoli cell function and suggest a mechanism by which Leydig cells could modulate Sertoli cell activity. Intratesticular administration of opiate antagonists inhibits testosterone secretion both in vivo and in vitro. These observations suggest that Leydig cell-derived beta-endorphin may facilitate testosterone secretion either directly or indirectly. The finding of POMC and its derivative peptides in testis, ovary, adrenal, and placenta suggests that all steroid hormone-secreting organs in mammals may utilize this peptidergic system.

Expression of pro-opiomelanocortin-like gene in the testis and epididymis

Adrenocorticotropin (ACTH), beta-endorphin, and the melanocyte-stimulating hormones (MSHs), which are products of a common precursor, pro-opiomelanocortin (POMC), are present in a variety of tissues other than pituitary. The recent detection of immunoreactive POMC-derived peptides in the male reproductive tract raised the possibility that these hormones might regulate reproductive function. To determine whether the low concentrations of POMC-derived peptides in the male reproductive tract are synthesized locally and are not contaminants from blood, we have demonstrated POMC-like gene expression in both testis and epididymis. The identification of cells in testis capable of synthesizing POMC mRNA was established by showing the presence of this mRNA in mouse Leydig cell lines (TM3 and I10A). The hybridizing species of POMC-like mRNA in the testis, epididymis, and Leydig cell lines (TM3 and I10A) were approximately 150 bases shorter than those in the pituitary or hypothalamus but were similar in size to that in the amygdaloid nucleus of rat brain. The concentration of POMC-like mRNA in the testis is almost as high as that in the hypothalamus. This finding is quite unexpected because the concentrations of POMC-derived peptides in the testis were 2-3 orders of magnitude lower than those in the hypothalamus. The demonstration of a POMC-like gene expression in male reproductive tissues suggests that POMC-derived peptides are synthesized in Leydig cells and epididymis. These observations are consistent with the postulate that POMC-derived peptides may exert paracrine and/or autocrine effects in these organs.