Male Reproductive Function Is Not Affected in Prolactin Receptor-Deficient Mice

0013-7227/03/$15.00/0 Printed in U.S.A. Endocrinology 144(9):3779 –3782 Copyright © 2003 by The Endocrine Society doi: 10.1210/en.2003-0409 Male Reproductive Function Is Not Affected in Prolactin Receptor-Deficient Mice NADINE BINART, NATHALIE MELAINE, CHARLES PINEAU, HENRI KERCRET, ANNE MARIE TOUZALIN, PRUNE IMBERT-BOLLORÉ, PAUL A. KELLY, AND BERNARD JÉGOU Hormone Targets, Institut National de la Santé et de la Recherche Médicale Unité 584 (N.B., P.I-B., P.A.K.), Faculté de Médecine Necker-Enfants Malades, 75015 Paris, France; and Groupe d’Etude de la Reproduction chez le Mâle-Institut National de la Santé et de la Recherche Médicale Unité 435 (N.M., C.P., H.K., A.M.T., B.J.), Université de Rennes 1, 35042 Rennes Cedex, Bretagne, France Mice with a targeted disruption of the prolactin (PRL) receptor gene were used to study the physiological role of PRL in the control of the male reproductive function. Fertility parameters as well as body and reproductive organ weights (epididymis and testes) were unaffected in PRL receptor knockout mice. Testicular histology and sperm reserves were also normal. Compared with wild-type animals, knockout mice W HEREAS PROLACTIN (PRL) has long been known to be the hormone responsible for mammary gland development and lactation in females, its role in the male has puzzled investigators ever since it has been shown to be present in the anterior pituitary. Initially, no clear function could be ascribed to PRL in male mammals, including humans (1, 2). However, more recent data have suggested that, generally, this hormone positively modulates several aspects of testicular function. Thus, PRL has been presented as being involved in the maintenance of cellular morphology (3) and in the up-regulation of LH receptor number on Leydig cells (4, 5). Along with LH, it has also been proposed to be implicated in the stimulation of steroidogenesis and androgen production (5–7), whereas, in contrast, it could be involved in the inhibition of aromatase activity (8). In vitro, PRL has been shown to increase FSH receptor number in Sertoli cells (9). It has also been suggested that PRL is involved in the rate of spermatocyte-spermatid conversion (3). Moreover, several in vitro effects on spermatozoa have been reported: a rise in calcium binding and/or transport of ejaculated and epididymal spermatozoa (10), an increase in energy metabolism (11), a maintenance of mobility and attachment to the oocyte (12), and a reduction in the time required to achieve capacitation (12). PRL also has metabolic effects on sex accessory organs (13–15). The effects on prostate include increased levels of androgen receptors (16, 17), involvement in estrogeninduced inflammation (18), increased epithelial secretory function (19, 20), and augmented energy metabolism. Stimulation of the level of IGF-I and its receptor has been also reported in the prostate (17). In addition to these in vitro data, it has been shown that, in the mouse, congenital PRL deficiency caused by recessive mutations at the pit-1 locus (Snell dwarf; Ames dwarf) is Abbreviations: hCG, Human chorionic gonadotropin; KO, knockout; PRL, prolactin; PRLR, PRL receptor. had no significant difference in basal plasma LH, FSH, and testosterone levels, and the weight of seminal vesicles and prostate was unaffected. Moreover, no alteration was detected in human chorionic gonadotropin-induced testosterone levels. It is concluded that the absence of PRL signaling is not detrimental to male testicular function and to fertility in the mouse. (Endocrinology 144: 3779 –3782, 2003) associated with reduced testosterone levels, a decrease in testicular LH and PRL receptor (PRLR) number, and a severe suppression of fertility (21, 22). However, these effects may well result from a drop in circulating gonadotropin levels observed in these studies. In contrast, the model of PRL knockout (KO) mouse has allowed the demonstration that, if PRL has a physiological role in the control of LH release and in the regulation of the growth of accessory reproductive glands, it does not seem to be directly required for the maintenance of circulating testosterone and fertility (23). The development of PRLR KO mice (24) has allowed us in the present study to reinvestigate the possible involvement of PRL in testicular function. We demonstrate that none of the male reproductive tract organ parameters or functions investigated was affected in this model. Materials and Methods Animals and mating trials The animals were produced by crossing animals heterozygous for the PRLR. Mice were housed under normal laboratory conditions in a 12-h light, 12-h dark cycle (0700 –1900). The temperature was controlled (21 C), and the animals had free access to tap water and standard pelleted animal food. The progeny was classified by PCR analysis of DNA extracted from tails clipping as described previously (25). After reaching adulthood (2–3 months of age), each male was placed for 30 d in a cage with two virgin females, and then the females were checked daily for the presence of a vaginal plug. Mating behavior (frequency of mounting and copulation) was analyzed, and immediately after parturition the size of the litter was recorded. The local committee on animal care approved all animal protocols. Human chorionic gonadotropin (hCG) test Ten PRLR KO and 10 wild-type mice were chosen at random and treated with an ip injection of hCG (Organon, Puteaux, France) in PBS, at 15 IU/animal. Controls (n ⫽ 10) were injected with PBS alone. Two hours after injection, all animals were decapitated, the blood collected, and the plasma separated and stored at ⫺20 C for hormones assays. 3779 3780 Endocrinology, September 2003, 144(9):3779 –3782 Binart et al. • Brief Communications forced by our data, which did not show any change in body weight of young KO animals (31.90 ⫾ 0.43/32.80 ⫾ 0.47 for ⫹/⫹ mice). No change was seen in testis, epididymis, seminal vesicle, or prostate weights, and testis histology was normal (Fig. 1). Moreover, sperm reserves were similar to those of controls (Fig. 2). Fertility study Neither the frequency of mounting and copulation nor the number of observed vaginal plugs in wild-type females mated to PRLR KO or to wild-type males was changed, indicating a normal mating behavior. All PRLR KO males similar to wild-type males were fertile (100% fertile, average litter size 8.2 ⫾ 0.3, n ⫽ 22; and 8.7 ⫾ 0.2, n ⫽ 15, respectively), and they continued to produce litters of normal size as they grew older. In contrast to our previous observation suggesting a delay of male fertility (24), no change of this parameter was seen in close studies. Hormonal status Pituitary hormones. Basal plasma FSH and LH levels were not significantly changed in PRLR KO vs. wild-type males (Table 1). Testosterone levels. Testosterone levels did not differ significantly between genotypes (Fig. 3). In agreement with these observations, the seminal vesicles and prosta (...truncated)