Immunoelectron microscopic localization of relaxin in endometrial gland cells of the pregnant guinea pig

Nucleic acid sequence of feline preprorelaxin and its localization within the feline placenta

The cat placenta is known to secrete large amounts of relaxin. We employed uteroplacental tissue at approximately Day 35 of gestation to determine the nucleic acid sequence of feline preprorelaxin using reverse transcription- and rapid amplification of cDNA ends-polymerase chain reaction. Feline preprorelaxin cDNA was found to consist of 540 base pairs encoding a protein of 180 amino acids (aa). We identified a signal peptide of 25 aa, a B domain of 33 aa, a C domain of 98 aa, and an A domain of 24 aa. The putative receptor binding region in the N'-terminal part of the B domain contained one substitution from the classical GRELVR motif (L-->F). Feline preprorelaxin shared highest homology with porcine and equine preprorelaxin. Northern analysis revealed a specific 1-kilobase transcript present in total RNA of feline uteroplacental tissue but not of liver tissue. Nonradioactive in situ hybridization was used to localize relaxin mRNA, and immunohistochemistry was used to localize the relaxin hormone and cytokeratin, in tissues of the feto-maternal interface recovered from two queens at Day 35 of gestation. Specific hybridization signals for relaxin mRNA were exclusively detected in cells located in the lamellar placental labyrinth but were absent from other placental and nonplacental uterine parts. The cells expressing relaxin mRNA also displayed immunoreactivity for cytokeratin and were, therefore, identified as trophoblast cells. Immunoreactive relaxin colocalized in those placental areas expressing relaxin mRNA. Trophoblast cells located at the villous chorioallantoic tips invading the endometrium and extravillous trophoblast cells in the junctional placental zone were devoid of relaxin.

Effects of estradiol and progesterone on accumulation of relaxin- and carbohydrate-containing granules in endometrial gland cells of the guinea pig

Guinea pigs were spayed and given various regimens of injections of estradiol and progesterone. The following were monitored in each animal: pubic separation (relaxin stimulation), resorption of the vaginal membrane (estrogen priming), and the presence of PAS-positive granules and/or relaxin in endometrial gland cells (EGC). Injections of estradiol alone resulted in resorption of the vaginal membrane, accumulation of PAS-positive granules in EGC of all animals, and accumulation of relaxin in EGC of two of four animals; but they did not cause pubic separation. Progesterone injections did not result in resorption of the vaginal membrane, separation of pubes, or accumulation of PAS-positive granules; however, one of three animals demonstrated a few EGC that contained relaxin. Animals that received both estradiol and progesterone exhibited PAS-positive granules and relaxin in EGC as well as separated pubes, but did not have resorbed vaginal membranes. Upon examination with the electron microscope, EGC from animals that received estradiol alone exhibited remarkable numbers of secretory granules that contained a carbohydrate-rich material. Secretory granules were not prominent in EGC from animals that received progesterone alone. Estradiol and progesterone injections resulted in accumulation of secretory granules in EGC that contained relaxin and a carbohydrate-rich material. The observations that estradiol and progesterone induce relaxin production in EGC support the hypothesis that uterine relaxin plays an important role in pregnancy and/or parturition in the guinea pig.

Immunochemical and cytochemical studies of relaxin-containing cells in the guinea pig uterus

Uteri and ovaries from cycling, pregnant, and lactating guinea pigs were studied for immunolocalization of relaxin with the light microscope. Endometrial gland cells (EGC) from the same group of animals were examined in the electron microscope for the presence of secretory granules. Those EGC that exhibited high numbers of granules were stained either for relaxin with the protein A colloidal gold method or for carbohydrate with the thiocarbohydrazide technique. Relaxin was found in EGC from middle and late pregnant animals but was not detected in ovaries or uteri from cycling animals. While cytoplasmic granules were noted in most EGC from cycling animals examined, the number of granules was greatest in uteri from estrus and proestrus animals. Granules in EGC from estrus animals contained a carbohydrate-rich material but did not contain relaxin. Endometrial gland cells from animals in early to middle stages of pregnancy (days 15 and 30) contained limited numbers of granules, almost all of which contained carbohydrate. At day 45 of pregnancy, EGC containing many granules were noted. The majority of granules contained relaxin; however, a significant number of EGC contained carbohydrate-rich granules. Infrequently, EGC were noted that contained two populations of granules, and these two populations were assumed to be made up of relaxin-containing and carbohydrate-rich granules. EGC from animals on day 60 of pregnancy typically contained granules, and the majority of these contained relaxin. Carbohydrate-rich granules were observed in EGC of the day 60 animals but were smaller in diameter and were noted in much lower numbers than the relaxin-containing granules. Endometrial gland cells from lactating animals infrequently contained granules. These studies are consistent with the hypothesis that the uterus is the primary source of relaxin in the guinea pig and that relaxin plays an important role in pregnancy and parturition of this species. The observations implicate endometrial glands and their products in the physiology of the cycling animal as well as the pregnant and parturient animal.