Novel vasopressin gene-related transcripts in rat testis

Kidney collecting duct-derived vasopressin is not essential for appropriate concentration or dilution of urine

We have previously shown that kidney collecting ducts make vasopressin. However, the physiological role of collecting duct-derived vasopressin is uncertain. We hypothesized that collecting duct-derived vasopressin is required for the appropriate concentration of urine. We developed a vasopressin conditional knockout (KO) mouse model wherein Cre recombinase expression induces deletion of arginine vasopressin (Avp) exon 1 in the distal nephron. We then used age-matched 8- to 12-wk-old Avp fl/fl;Ksp-Cre(-) [wild type (WT)] and Avp fl/fl;Ksp-Cre(+) mice for all experiments. We collected urine, serum, and kidney lysates at baseline. We then challenged both WT and knockout (KO) mice with 24-h water restriction, water loading, and administration of the vasopressin type 2 receptor agonist desmopressin (1 µg/kg ip) followed by the vasopressin type 2 receptor antagonist OPC-31260 (10 mg/kg ip). We performed immunofluorescence and immunoblot analysis at baseline and confirmed vasopressin KO in the collecting duct. We found that urinary osmolality (UOsm), plasma Na+, K+, Cl-, blood urea nitrogen, and copeptin were similar in WT vs. KO mice at baseline. Immunoblots of the vasopressin-regulated proteins Na+-K+-2Cl- cotransporter, NaCl cotransporter, and water channel aquaporin-2 showed no difference in expression or phosphorylation at baseline. Following 24-h water restriction, WT and KO mice had no differences in UOsm, plasma Na+, K+, Cl-, blood urea nitrogen, or copeptin. In addition, there were no differences in the rate of urinary concentration or dilution as in WT and KO mice UOsm was nearly identical after desmopressin and OPC-31260 administration. We conclude that collecting duct-derived vasopressin is not essential to appropriately concentrate or dilute urine.NEW & NOTEWORTHY Hypothalamic vasopressin is required for appropriate urinary concentration. However, whether collecting duct-derived vasopressin is involved remains unknown. We developed a novel transgenic mouse model to induce tissue-specific deletion of vasopressin and showed that collecting duct-derived vasopressin is not required to concentrate or dilute urine.

Urocortins are present in the rat testis

The synthesis and release of testosterone (T) depends both on circulating luteinizing hormone (LH) and on an array of testicular factors whose role remains incompletely understood. Corticotropin-releasing factor (CRF) had been reported in the rat testes, where it was thought to inhibit T secretion. However, the discovery that the CRF-related peptides urocortins (Ucns), of which there are currently three subtypes (Ucn 1, 2 and 3), cross-react with many reagents previously used to detect CRF, has cast doubt on this concept. Here we show that while CRF was readily measurable in rat hypothalami (which served as controls), signals for this peptide were barely detectable in total RNA extracted from the testes. On the other hand, microarray, RT-PCR and real-time quantitative RT-PCR (qRT-PCR) analyses all indicated strong signals for Ucn 1 in the male gonads, with weaker levels of Ucn 2 and 3 mRNA gene expression. Results obtained for Ucn 1 gene expression were corroborated by immunohistochemical detection, which appeared restricted to Leydig cells. Finally, to investigate possible changes in testicular Ucn 1 levels induced by homeostatic challenges, we measured them in rats exposed to alcohol. We observed that indeed, the intragastric injection of this drug significantly increased testicular Ucn 1, but not Ucn 2, Ucn 3, CRF, CRFR1 or CRFR2 mRNA levels. Collectively, these results provide novel information regarding the presence of CRF-like peptides in the adult male rat testis.

Hypo-osmotic shock induces nuclear export and proteasome-dependent decrease of UBL5

The osmolarity of body fluid is strictly controlled through the action of diuretic hormones, which are secreted in the hypothalamus. In the mammalian brain, ubiquitin-like 5 (UBL5) is expressed in oxytocin- and vasopressin-positive neurons in the hypothalamus, and these neurons play a role in regulating osmolarity. We examined the dynamics of UBL5 levels in response to hyper- or hypo-osmotic conditions. Hypo-osmotic conditions led to significantly reduced levels of UBL5 both in brain slices from the hypothalamus and in NIH-3T3 cells. This decrease in UBL5 was transcription-independent and proteasome-dependent. Time-course immunocytochemical studies using exogenous UBL5 revealed that the protein was exported from the nucleus under hypo-osmotic conditions and decreased in a proteasome-dependent manner. This report is the first to describe changes in the intracellular and subcellular localization of UBL5 in response to hypo-osmotic conditions. Our results imply osmoregulation of UBL5.

Presence in mouse Sertoli cell-conditioned medium of a factor that expresses AVP-like inhibition of steroidogenesis by mouse Leydig cells in long-term culture

The influence of spent medium from immature mouse Sertoli cells (SCM) on testosterone production by purified Leydig cells was investigated and compared to that of AVP, a potent local modulator of Leydig cell steroidogenesis. SCM inhibited in a dose-dependent manner the hCG-stimulated testosterone production, but was ineffective in basal conditions. As is known for AVP, (i) a lag period of 72 h was prerequisite for SCM to inhibit Leydig cell function; (ii) the main effect of SCM was located at a step beyond the receptor-adenylate cyclase system, since the hCG- and 8-bromo-cAMP-stimulated testosterone productions were similarly affected. The possibility that the effect of SCM may be related to AVP-like molecule(s) is also supported by the observations that at maximal concentrations the inhibitory effects of AVP and SCM were not additive and that the inhibition of testosterone production was largely (65%) reversed by the presence of [(beta-mercapto-beta, beta-cyclopentamethylenepropionyl, O-Me-Tyr2,Arg8)-vasopressin], a selective vasopressor antagonist. These data indicate that Sertoli cells produce in vitro potent inhibitory factors of Leydig cell steroidogenesis. They provide additional evidence that one of these bioactive factors has an effect on Leydig cell function similar to that of AVP.

Vasopressin and oxytocin production by non-neuroendocrine lung carcinomas: an apparent low incidence of gene expression

In previous studies we have demonstrated the high incidence of vasopressin gene expression as a characteristic feature of small-cell carcinoma of the lung. In the present study we examined expression of this gene in non-neuroendocrine tumors to determine if vasopressin production is a common feature of all lung tumors. We carried out the immunohistochemical evaluation of 22 non-neuroendocrine tumors (12 adenocarcinomas and 10 squamous-cell carcinomas) with antibodies to vasopressin, to oxytocin, and to their related neurophysins. The antibody preparations directed against vasopressin, oxytocin, or oxytocin-associated human neurophysin did not react with any of the tumors examined. Of two monoclonal antibodies to vasopressin-associated human neurophysin used, one did not react with any of the tumors, while the other stained neoplastic cells in only one adenocarcinoma and one squamous-cell carcinoma. These findings, taken with previous reports, indicate that among lung carcinomas, a high incidence of vasopressin/oxytocin gene expression is confined to neuroendocrine tumors.

Biosynthesis of vasopressin by gastrointestinal cells of Brattleboro and Long-Evans rats

The distribution of vasopressin, provasopressin, vasopressin-associated neurophysin, and vasopressin-associated glycopeptide was determined immunohistochemically in the gastrointestinal system of Brattleboro and Long-Evans rats. Cells containing immunoreactivity for vasopressin, provasopressin, neurophysin, and glycopeptide were detected in the same cell types of the stomach and duodenum, while selected cells in the duodenum contained only immunoreactive glycopeptide. Unlike that in the hypothalamus, staining for neurophysin in the gastrointestinal tract was sensitive to fixation. These findings indicate that vasopressin is produced by cells in the rat gastrointestinal system and suggest the existence of synthetic pathways different from those found in hypothalamic neurons.

Oxytocin gene expression in rat uterus

The neurohypophyseal hormone oxytocin (OT) is the most potent uterotonic agent known and is used to induce labor. Yet, endogenous circulating OT appears not to participate in the induction of labor. As shown here, the finding of OT messenger RNA and peptide in the uterus suggests a solution for this paradox. During gestation, rat uterus OT messenger RNA increased more than 150-fold and, at term, exceeded hypothalamic OT messenger RNA by 70-fold. Thus, during parturition, OT may act primarily as a local mediator and not as a circulating hormone.