The Endocannabinoid System and the Neuroendocrine Control of Hydromineral Balance

Endocannabinoids (ECBs) are ubiquitous lipophilic agents, and this characteristic is consistent with the wide range of homeostatic functions attributed to the ECB system. There is an increasing number of studies showing that the ECB system affects neurotransmission within the hypothalamic neurohypophyseal system. We provide an overview of the primary roles of ECBs in the modulation of neuroendocrine function and, specifically, in the control of hydromineral homeostasis. Accordingly, the general aspects of ECB‐mediated signalling, as well as the specific contributions of the central component of the ECB system to the integration of behavioural and endocrine responses that control body fluid homeostasis, are discussed.     

Suckling and Salsolinol Attenuate Responsiveness of the Hypothalamic‐Pituitary‐Adrenal Axis to Stress: Focus on Catecholamines,Corticotrophin‐Releasing Hormone,Adrenocorticotrophic Hormone,Cortisol and Prolactin Secretion in Lactating Sheep

In mammals, the responsiveness of the hypothalamic‐pituitary‐adrenal (HPA) axis to stress is reduced during lactation and this mainly results from suckling by the offspring. The suckling stimulus causes a release of the hypothalamic 1‐metyl‐6,7‐dihydroxy‐1,2,3,4‐tetrahydroisoquinoline (salsolinol) (a derivative of dopamine), one of the prolactin‐releasing factors. To investigate the involvement of salsolinol in the mechanism suppressing stress‐induced HPA axis activity, we conducted a series of experiments on lactating sheep, in which they were treated with two kinds of isolation stress (isolation from the flock with lamb present or absent), combined with suckling and/or i.c.v infusion of salsolinol and 1‐methyl‐3,4‐dihydro‐isoqinoline (1‐MeDIQ; an antagonistic analogue of salsolinol). Additionally, a push–pull perfusion of the infundibular nucleus/median eminence (IN/ME) and blood sample collection with 10‐min intervals were performed during the experiments. Concentrations of perfusate corticotrophin‐releasing hormone (CRH) and catecholamines (noradrenaline, dopamine and salsolinol), as well as concentrations of plasma adenocorticotrophic hormone (ACTH), cortisol and prolactin, were assayed. A significant increase in perfusate noradrenaline, plasma ACTH and cortisol occurred in response to both kinds of isolation stress. Suckling and salsolinol reduced the stress‐induced increase in plasma ACTH and cortisol concentrations. Salsolinol also significantly reduced the stress‐induced noradrenaline and dopamine release within the IN/ME. Treatment with 1‐MeDIQ under the stress conditions significantly diminished the salsolinol concentration and increased CRH and cortisol concentrations. Stress and salsolinol did not increase the plasma prolactin concentration, in contrast to the suckling stimulus. In conclusion, salsolinol released in nursing sheep may have a suppressing effect on stress‐induced HPA axis activity and peripheral prolactin does not appear to participate in its action.