The hypothalamic CB1 receptor participates in reproductive axis impairment induced by endotoxemia

PABLO NICOLÁS SURKIN; VALERIA RETTORI; JAVIER FERNANDEZ-SOLARI; SOFIA LUDMILA GALLINO; ANDREA DE LAURENTIIS; CÉSAR ANGEL OSSOLA; JUAN CARLOS ELVERDIN

NIH Campus, Bethesda, MD, USA.

Simposio; Marijuana and Cannabinoids: A Neuroscience Research Summit; 2016

National Institutes of Health

The inhibitory effect of endotoxemia on reproductive system is fully characterized, as well as the modulation of sexual hormones levels by endocannabinoids. However, little is known about the role of the endocannabinoid system (ECS) on the effects of endotoxemia on reproductive hypothalamic-hypophyseal (HP) axis. The hypothesis of the study consists in the belief that ECS allows the inhibition of the reproductive system during endotoxemia. Considering the following, the objective of this study was to evaluate the participation of the hypothamic cannabinoid receptor CB1 (CB1R) on HP axis when rats were submitted to endotoxemia. Sprague Dawley rats were implanted with intracerebroventricular (icv) cannulas at the 3rd ventricle by stereotaxis. Seven days after surgery a silastic catheter was introduced in the right jugular vein, allowing repeated blood sampling. The next day, rats were treated via icv with a CB1R antagonist, (AM251, 500ng/5ul) or its vehicle, followed by an intraperitoneal (ip) injection of LPS (5mg/kg) or its vehicle 15 minutes later. Blood samples were obtained at 0, 30, 60, 90 and 180 minutes after LPS challenge. Plasma TNFα by ELISA and corticosterone and LH by RIA were determined. In other set of experiments, rats implanted with icv cannulas, were administrated with AM251 or its vehicle (icv) and/or LPS or its vehicle (ip) and 1 hour post LPS challenge rats were euthanized and medial basal hypothalamus and adenohypophysis were rapidly removed. The explants were incubated in Krebs/Ringer buffer in a Dubnoff bath at 37ºC with CO2/O2 during 15 minutes. Media were collected to measure LHRH and PGE2 released from hypothalamic and hypophyseal explants by RIA.Plasma corticosterone levels were augmented when treated with LPS, but CB1 blockade did not induce changes. In the other hand, CB1 blockade increased plasmatic TNFα levels in LPS treated rats. LHRH release from hypothalamic explants was inhibited by LPS and this effect is in concordance with plasma LH decrease. The blockade of CB1 hypothalamic receptor partially prevented this inhibitory effect of LPS. As expected, endotoxemia augmented PGE2 release from hypothalamic explants, and this effect was higher when CB1 receptor was blocked. Moreover, the blockade of CB1R allows/unmask the significant increase of PGE2 release from adenohypophysis after LPS treatment.Our results indicate that the inhibitory effects of LPS on LH release are partially dependent on the hypothalamic CB1R. Althoug LPS induced-endotoxemia increases stress markers and the hypothalamic CB1R seems not to be the main controller our results suggest an inhibitory tone of the endocannabinoid system on inflammatory response at systemic, hypothalamic and hypophyseal levels. Our findings help to understand the role of ECS on neuroimmunological mechanisms underlying fertility.