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In this study, the protein and mRNA expression of the short and long forms of Prolactin (PRL) receptors (PRL-R) were examined by means of Northern and Western blotting analyses in rat testicular Sertoli cells. Transcripts for the short and long forms of PRL-R were detected with specific probes, five major mRNA species of about 1.9, 2.6, 3.0, 3.7 and 5 kb for the short form and two of about 10 and 1.3 kb for the long form. Under reducing conditions, the use of a specific antibody for the short form revealed a major molecular species of approximately 45 kDa. Two groups of molecular species were detected for the long form, several bands with high molecular masses (110-300 kDa) and others about 45-60 kDa. Finally, the expression of the long form of PRL-R was shown to be hormonally regulated as it was inhibited by follicle stimulating hormone (FSH) (ED50 = 5 ng/ml). Together, the localisation of PRL receptors to Sertoli cells as well as the regulatory action of FSH on these receptors suggest that PRL and or (a) PRL-like activity(ies) might be considered as (a) potential regulator(s) of spermatogenesis.

This work was undertaken to determine variations in the 125I-labelled ovine prolactin (oPRL) binding in rat liver and mammary gland membranes, and to study the molecular forms of prolactin receptor in different physiological situations. Prolactin binding was determined using 125I-labelled oPRL in the 100,000 g pellet. 125I-Labelled oPRL was cross-linked to receptors in membranes from rat liver and mammary gland and subjected to SDS-PAGE under reducing conditions, followed by autoradiography of dried gels. In the mammary gland, the specific binding of oPRL to membranes, expressed as mean +/- S.E.M. fmol/mg protein increased from 1.36 +/- 0.24 on the day of dioestrus to 3.26 +/- 0.60 on the day of oestrus. It remained very low during pregnancy but increased during lactation to reach 4.78 +/- 0.99. In the liver, the specific binding of oPRL to membranes was higher than in the mammary gland on the days of dioestrus 1, dioestrus 2 and oestrus, but not on the day of pro-oestrus. It increased until day 14 of pregnancy when the specific binding of 125I-labelled oPRL was 17.01 +/- 0.30. Cross-linking revealed different molecular forms in the mammary glands and the liver. In the mammary gland we observed four prolactin-binding forms of 80, 50, 40 and 16 kDa, all of which were specific for prolactin. The 80, 50 and 40 kDa forms were also able to bind to a Concanavalin A-Sepharose column, indicating that these binding forms were glycosylated while the smaller one (16 kDa) appeared to be unglycosylated.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovine prolactin (oPRL) binding to liver membranes was studied during the estrous cycle in normal and in genetically hypoprolactinemic rats. Serum levels of hormones were measured by radioimmunoassay and prolactin (PRL) binding was determined using 125I-ovine PRL in the 100,000 X g pellet. Scatchard plots obtained were curvilinear throughout the estrous cycle in the normal rat. They were analyzed in reference to the co-operativity model and to the Hill model which give the factor delta and Hill's coefficient (nH), respectively. During the estrous cycle, delta values varied from 3.77 +/- 0.66 on the day of estrous to 13.48 +/- 1.34 on the day of proestrus at 16.00 h. At the same time, nH were 0.97 +/- 0.033 on the day of estrus and 0.72 +/- 0.025 on the day of proestrus at 16.00 h. On the other hand, the number of PRL receptors did not change significantly throughout the estrous cycle. Moreover, the dissociation of 125I-oPRL from its receptor was accelerated by the presence of native ovine oPRL. These results suggest the presence of a negative co-operativity which reached a maximum on the day of proestrus in the normal rat. This co-operativity during the estrous cycle was not found in liver from genetically hypoprolactinemic (IPL nude) rats, which present a total absence of lactation. The delta values did not vary significantly and were 6.52 +/- 1.30 on the day of estrus and 4.41 +/- 0.52 on the day of proestrus at 16.00 h. The difference between the two rat strains was statistically significant on the day of proestrus at 16.00 h for both delta and nH values.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovine prolactin (oPRL) binding to liver membranes was studied during pregnancy in normal and in genetically hypoprolactinemic rats. Prolactin (PRL) binding was determined using 125I-oPRL in the 100,000 x g pellet. Scatchard plots obtained changed throughout the pregnancy in the normal rat, being almost linear from days 2 to 10, becoming curvilinear (convex) on day 16, and linear again at the end of pregnancy. They were analyzed with reference to the co-operativity and Hill models, which give delta and nH, respectively. During pregnancy, delta values varied and were respectively 2.48 +/- 0.66, 1.84 +/- 0.64, 0.52 +/- 0.06 and 1.69 +/- 0.25 on days 3, 10, 16 and 22, and the delta value on day 16 was significantly different from other days; the nH value estimated on day 16 was 1.10 +/- 0.031. These results suggest the presence of a positive co-operativity on day 16 of pregnancy. Over the same period, a huge increase in the capacity occurred on day 10 and reached a maximum on day 14. It remained elevated until the day before parturition. In the IPL nude rat, the delta value (0.92 +/- 0.45) on day 16 was significantly different from that of normal rats and indicated an absence of positive co-operativity on this day in the IPL nude rat liver. This finding was confirmed by an nH value (0.99 +/- 0.39) close to 1. The PRL-binding capacity was similar to that of normal rats, except on day 14, where it was significantly decreased. These results are discussed in relation to hormonal variations during pregnancy, particularly with regard to serum PRL and placental lactogen values.(ABSTRACT TRUNCATED AT 250 WORDS)