No abstract

Our objective was to determine the effect of ovine interferon-t (IFN-t) on prolactin receptor (PRL-R) gene expression in the ovine endometrium. IFN-t is an embryonic cytokine which, via its paracrine anti-luteolytic activity, plays a critical role in maternal recognition of pregnancy in ruminants. Using ribonuclease protection assay procedures, we compared endometrial PRL-R mRNA levels in ewes that were intrauterine injected with either 2 mg bovine serum albumin or 2 mg recombinant ovine IFN-t on day 10 of the oestrous cycle (day 0 5 day of oestrus). IFN treatment significantly increased the abundance of both the long and short forms of PRL-R mRNA in the ovine uterus, but had no effect on the long:short form ratio. In situ hybridization experiments revealed that the increase in abundance of PRL-R mRNA in the uterus was localized to the glandular compartment of the endometrium. In pregnant ewes, a similar increase in PRL-R mRNA abundance was found to occur in ovine endometrium on days 14-15 post conception. Collectively, these data provided strong evidence that IFN-t modulates the level of lactogenic hormone receptor mRNA in the ovine uterus. Whether the effect of IFN-t on PRL-R expression is mediated directly or influenced, at least in part, by progesterone remains to be elucidated.

In dispersed rat Leydig cells, colchicine was found to stimulate basal cAMP production and testosterone secretion in a dose and time-dependent manner, but to a lesser extent than LH. However, these drugs are unable to stimulate adenylate cyclase activity in plasma membranes isolated from these cells. The amount of testosterone secreted at 150 min under the influence of colchicine and LH added simultaneously was not different from the amount produced during stimulation by LH alone. It is only after exposure of the cells for 1 hr to colchicine that the accumulation of cAMP in response to LH was inhibited; furthermore, both intracellular and medium testosterone accumulation in response to the hormone were reduced. Similar effects were observed with two other alkaloids, vinblastine and podophyllotoxin. The three drugs also inhibited the stimulation of testosterone secretion by 8-Br-cAMP or choleratoxin. These studies suggest that the state of microtubule polymerization and/or tubulin can influence the process of steroidogenesis in rat Leydig cells.

No abstract

Rat intestinal cells prepared from testes were incubated in the presence of different lutropin derivatives obtained by chemical modification of the amino groups. The cAMP accumulation and the testosterone biosynthesis were determined in the cell homogenates. Binding determinations were carried out by a radioligand receptor assay using tritiated methylated lutropin. The binding activities \ p=m-\ relative to native LH \ p=m-\ of three different derivatives obtained by reductive alkylation (methylated, ethylated and isopropylated LH) were in good agreement with the relative potencies assessed by their capacity to stimulate cAMP and testosterone production. Guanidinated LH (11 \p=m-\ NH2 groups modified) exhibited a binding activity and a relative potency relatively high with regard to cAMP accumulation (as compared with that of native LH). Its steroidogenic potency, however, was very low. When Leydig cells were incubated in the presence of native and guanidinated LH, the testosterone production was similar to that induced by the derivative alone, indicating that the derivative exerted a competitive inhibitory action preventing the stimulation of steroidogenesis by native LH. These results suggest that a guanidinated derivative is able to bind to the LH receptor and the complex so formed is able to be coupled with an adenylate cyclase pool (or cAMP compartment) which is not connected with the steroidogenic pathway.Chemical modification of the amino groups of lysine residues can be achieved in lutropin (luteiniz¬ ing hormone, LH) without loss or with only a partial loss of the biological activity, if the positive charge of these residues is not abolished (De la Llosa et al. 1974a; Liu et al. 1974). These derivatives have been tested by various bioassays, in vivo and in vitro. It has been shown that they are able to bind to the LH-receptors (Liu et al. 1974; De la Llosa-Hermier et al. 1977), to activate ovarian adenylate cyclase (Tertrin-Clary & De la Llosa 1978) and to stimulate steroidogenesis in the ovary. We considered it of interest to investigate the correlation between the succes¬ sive responses induced by these derivatives which are known to be consecutive steps in the mecha¬ nism of action of LH. Rat Leydig cells were used as biological material. As is well known, binding of lutropin to the receptors of Leydig cells is followed by activation of adenylate cyclase, and the subse¬ quent cyclic AMP accumulation is accompanied by stimulation of testosterone production. The data reported here show that a good correlation is observed for most of these derivatives in each of the three steps, but that at least in one case (guanidinatedLH), binding to the receptors and stimula¬ tion of adenylate cyclase do not result in a propor¬ tional increase in testosterone biosynthesis. In such a case an inhibitory effect of the derivative on the final action of the hormone could be expected and was demonstrated. Material and MethodsOvine LH was prepared in a highly purified state (biolo¬ gical potency: 2 x LH-NIHS11) in our labo...