We have previously shown that administration of antiprogestin (AP) type II RU486 to ovariectomized (OVX) rats on the morning of pro-oestrus decreases the magnitude of preovulatory gonadotrophin surge. This suggests that the effect of RU486 on LHRH-dependent gonadotrophin release may be independent of its ability to block progesterone actions. The aim of the present research was to study the possible site of RU486 action and to determine whether the gonadotrophin suppressive effect of APs RU486 and ZK299 is dependent on the oestrogen background. Intact or OVX rats in the morning of pro-oestrus were injected s.c. with 4 mg of RU486 or ZK299 (AP type I) at 0900 h on pro-oestrus. At 1830 h, serum concentration of FSH and LH and median eminence (ME) content of LHRH were determined. In the second experiment, the effect of RU486 and ZK299 on pituitary responsiveness to LHRH (100 ng, i.p.) and ME content of LHRH at 1830 h pentobarbital-blocked intact or OVX rats was evaluated. In the last study, the anterior pituitary release of FSH and LH from pro-oestrus or metoestrus donors incubated with or without LHRH (1, 10 or 100 nM) in the presence or absence of APs (20 nM) was evaluated. Both APs reduced serum FSH and LH levels at 1830 h on pro-oestrus in intact and OVX rats. The suppressive effect on gonadotrophin release brought about by AP treatment was also evidenced in PB-blocked intact and OVX rats. This suggested that the inhibitory effect of APs occurred, at least in part, at pituitary level. Furthermore, in the absence of the natural ligand, APs significantly reduced basal and LHRH-stimulated FSH and LH release from pro-oestrous but not from metoestrus pituitaries. In conclusion, these experiments have shown, both 'in vivo' and 'in vitro', that APs RU486 and ZK299 have suppressive effects at pituitary level on basal and LHRH-stimulated FSH and LH secretion, regardless of their antiprogestagenic activity, in pro-oestrus but not in metoestrus.
C Bellido, D Gonzalez, R Aguilar, and JE Sanchez-Criado
MT Martinez-Merlos, M Angeles-Castellanos, M Diaz-Munoz, R Aguilar-Roblero, J Mendoza, and C Escobar
Digestive and metabolic processes are entrained by restricted feeding (RFS) schedules and are thought to be potential elements of a food-entrained oscillator (FEO). Due to the close relationship of leptin with metabolic regulation and because leptin is a relevant communication signal of the individual's peripheral metabolic condition with the central nervous system, we explored whether leptin is an endogenous entraining signal from the periphery to a central element of an FEO. First we characterized in the rat the diurnal rhythm of serum leptin (in rats fed ad libitum (AL)), its adjustment to an RFS and the influence of fasting after RFS, or RFS followed by AL feeding and then total food deprivation (RF-AF) in the persistence of this fluctuating pattern. We also explored the response of free fatty acids and stomach weight under the same entraining conditions. We compared the metabolic response with the behavioral expression of drinking anticipatory activity (AA) under the same conditions. Finally, we tested the effect of daily i.c.v administration of leptin as a putative entraining signal for the generation of AA.Metabolic parameters responded to food entrainment by adjusting their phase to mealtime. However, leptin and free fatty acid rhythms persisted only for a few cycles in fasting conditions and readjusted to the light-darkness cycle after an RF-AF protocol. In contrast, behavioral food-entrained rhythms persisted after both fasting manipulations. Daily leptin i.c.v. administration did not produce AA, nor produce changes in the behavioral free-running rhythm. Stomach weight indicated an adaptive process allowing an extreme stomach distension followed by a slow emptying process, which suggests that the stomach may be playing a relevant role as a storage organ. In conclusion, metabolic signals here studied respond to feeding schedules by adjusting their phase to mealtime, but do only persist for a few cycles in fasting. Leptin does not produce AA and thus is not an entraining signal for FEO. The response of metabolic signals to feeding schedules depends on different mechanisms than the expression of AA.
C Aceves, C Escobar, R Rojas-Huidobro, O Vazquez-Martinez, T Martinez-Merlos, R Aguilar-Roblero, and M Diaz-Munoz
Restricted feeding schedules (RFSs) produce a behavioral activation known as anticipatory activity, which is a manifestation of a food-entrained oscillator (FEO). The liver could be playing a role in the physiology of FEO. Here we demonstrate that the activity of liver selenoenzyme deiodinase type 1 (D1), which transforms thyroxine into triiodothyronine (T3), decreases before food access and increases after food presentation in RFSs. These changes in D1 activity were not due to variations in D1 mRNA. In contrast, a 24 h fast promoted a decrease in both D1 activity and mRNA content. The adjustment in hepatic D1 activity was accompanied by a similar modification in T3-dependent malic enzyme, suggesting that the local generation of T3 has physiological implications in the liver. These results support the notion that the physiological state of rats under RFSs is unique and distinct from rats fed freely or fasted for 24 h. Data also suggest a possible role of hepatic D1 enzyme in coordinating the homeorhetic state of the liver when this organ participates in FEO expression.
J E Sánchez-Criado, J Martín de las Mulas, C Bellido, R Aguilar, and J C Garrido-Gracia
The selective oestrogen receptor modulator (SERM) tamoxifen (TX) has agonist/antagonist actions on LH secretion in the rat. Whereas in the absence of oestrogens TX elicits progesterone receptor (PR)-dependent GnRH self-priming, it antagonizes oestrogen-stimulatory action on LH secretion. The aim of these experiments was to explore whether TX treatment-induced differential expression of oestrogen receptor (ER)α and ERβ in the gonadotrope may determine its agonist effect on LH secretion. In the first experiment, basal LH secretion, GnRH-stimulated LH secretion and PR-dependent GnRH self-priming were determined in incubated pituitaries from ovariectomized (OVX) rats treated with oestradiol benzoate (EB), TX or raloxifene (RX). Cycling rats in metoestrus or pro-oestrus were used as basic controls. As in pro-oestrus, pituitaries from OVX rats treated with EB exhibited GnRH-stimulated LH secretion, immunohistochemical PR expression and GnRH self-priming. While RX had no effect on these parameters, TX induced PR expression and GnRH self-priming. GnRH self-priming was absent in pituitaries incubated with the antiprogestin ZK299. In the second experiment, we evaluated the immunohistochemical expression of ERα and ERβ in gonadotropes of cycling rats and OVX rats treated with EB, TX or RX. We found that while ERα expression was similar in all six groups, ERα expression was oestrous cycle dependent. Moreover, ERα expression in gonadotropes of TX-treated rats was as high as that found in pro-oestrus, while ERα expression in the gonadotropes of RX-treated rats was lower than in metoestrous or pro-oestrous pituitaries. These results suggest that, in the absence of the cognate ligand, TX, unlike RX, may regulate LH secretion through the ERα subtype in gonadotropes.
F Gaytan, C Morales, C Bellido, R Aguilar, Y Millan, J Martin De Las Mulas, and JE Sanchez-Criado
Preovulatory surges of both prolactin (PRL) and progesterone have been suggested to be necessary for the induction of apoptosis in the regressing corpus luteum of the cyclic rat. The aim of these experiments was to study whether the administration of PRL and/or progesterone on the morning of pro-oestrus reproduces the regressive changes that happen in the cyclic corpus luteum (CL) during the transition from pro-oestrus to oestrus, and to analyse the temporal relationships between two characteristic features of structural luteolysis (luteal cell apoptosis and accumulation of macrophages). Cyclic rats (treated at 0900 h with an LHRH antagonist to block LH secretion) were injected at 1000 h with PRL and progesterone and killed at 0, 30, 60, 90 and 180 min after treatment. The number of apoptotic cells increased progressively from 60 min after treatment onward in hormone-treated rats, whereas the number of macrophages did not change throughout the period of time considered. Rats injected with PRL plus progesterone showed significantly greater numbers of apoptotic cells than those injected with PRL alone. The luteolytic effects of progesterone were in keeping with the presence of luteal endothelial cells showing progesterone receptor (PR) immunoreactivity in pro-oestrus. Treatment of rats during dioestrus and pro-oestrus with the specific antioestrogens LY117018 and RU58668 decreased the luteolytic effects of PRL and progesterone and the number of luteal endothelial cells immunostained for PR. These results strongly suggest that the preovulatory PRL surge and the preovulatory increase in progesterone together trigger structural regression of the corpus luteum. This seems to be dependent on oestrogen-driven cyclic changes in PRs in luteal endothelial cells.
J E Sánchez-Criado, J Martín de las Mulas, C Bellido, V M Navarro, R Aguilar, J C Garrido-Gracia, M M Malagón, M Tena-Sempere, and A Blanco
In the rat, oestrogen is a key regulator of gonadotrophin synthesis and release through activation of oestrogen receptors (ERs). Gonadotropes express α and β isoforms of ER and both can activate transcription in response to oestrogen. These experiments were aimed at evaluating the relative contribution of ERα and ERβ on gonadotrope morphology, progesterone receptor (PR) expression and LH secretion. Ovariectomized rats were daily injected over 3 days with 25 μg oestradiol benzoate, 0.3 or 1.5 mg of the selective ERα agonist propylpyrazole triol (PPT) with or without 1.5, 3.0 or 4.5 mg of the selective ERβ agonist diarylpropionitrile (DPN), DPN alone, and 0.3 or 3 mg of tamoxifen. Controls were given 0.2 ml oil. Serum concentration and pituitary content of LH, gonadotrope PR expression, pituitary PR content, and gonadotrope morphology were analyzed by RIA, immunohistochemistry, Western blotting and light and electron microscopy, respectively. Results showed that PPT reversed all consequences of ovariectomy, DPN mimicked the effects of PPT except for its LH-releasing action and tamoxifen had ERα-like responses. When combined with PPT, DPN attenuated ERα effects without interfering with its LH-releasing activity. Oestradiol benzoate had similar effects to those of combined PPT and DPN. It is suggested that (i) the structural reorganization of the cytoplasmic organelles provided by oestrogen, and the shrinkage of the ovariectomy-induced hypertrophy of gonadotropes, which precedes the expression of PR, are evoked by ERα and modulated, in a ying–yang fashion, by ERβ; and (ii) the oestrogen-dependent exocytosis of LH, the final step in the secretory process, is dependent on ERα exclusively.