Hypothalami, anterior pituitary gland segments and adrenal glands were removed from female Wistar-derived rats decapitated at various times of the day. Blood and tissue hormone concentrations were measured and the tissues challenged with appropriate stimuli in vitro. Both bioactive and immunoreactive corticotrophin-releasing factor (CRF) content of the hypothalami were significantly higher in the evening than in the morning, as was the basal release of bioactive CRF in vitro. The response of the hypothalami to serotonin or acetylcholine added in vitro did not change with time of day. Basal bioactive and immunoreactive adrenocorticotrophin (ACTH) release from the anterior pituitary gland was significantly increased in the evening, as was the response to synthetic ovine CRF in vitro. Plasma ACTH concentrations in intact rats given crude CRF (hypothalamic extract) in vivo were higher in the evening at all times after injection tested, but this difference was markedly reduced in animals with mediobasal hypothalamic lesions. Corticosterone released basally from adrenal glands in vitro was significantly increased in the evening and the response to added ACTH 1–24 was slightly enhanced. For adrenal glands removed from lesioned rats, the pattern was reversed, corticosterone release in vitro being lower in the evening for all doses of ACTH added. Similarly in vivo, in intact rats given ACTH 1–24, plasma corticosterone concentrations and corticosterone release in vitro from adrenal glands removed after the injection were higher in the evening. After the placement of basal hypothalamic lesions, the situation was reversed, the response to ACTH administration in vivo being greater in the morning. The peaks in plasma concentrations of ACTH and corticosterone occurred 1 h later than the peak in hypothalamic CRF release. Therefore, it appears that the timing of the diurnal variation in plasma levels is dictated by the hypothalamus, but circadian changes in the output and responsiveness of the pituitary gland to CRF and the adrenal glands to ACTH play a major role in determining the amplitude of the rhythm.

Background and PurposeRaised serum concentrations of the sympathetic co‐transmitter neuropeptide Y (NPY) are linked to cardiovascular diseases. However, the signalling mechanism for vascular smooth muscle (VSM) constriction to NPY is poorly understood. Therefore, the present study investigated the mechanisms of NPY‐induced vasoconstriction in rat small mesenteric (RMA) and coronary (RCA) arteries.Experimental ApproachThird‐order mesenteric or intra‐septal arteries from male Wistar rats were assessed in wire myographs for isometric tension, VSM membrane potential and VSM intracellular Ca2+ events.Key ResultsNPY stimulated concentration‐dependent vasoconstriction in both RMA and RCA, which was augmented by blocking NO synthase or endothelial denudation in RMA. NPY‐mediated vasoconstriction was blocked by the selective Y1 receptor antagonist BIBO 3304 and Y1 receptor protein expression was detected in both the VSM and endothelial cells in RMA and RCA. The selective Gβγ subunit inhibitor gallein and the PLC inhibitor U‐73122 attenuated NPY‐induced vasoconstriction. Signalling via the Gβγ–PLC pathway stimulated VSM Ca2+ waves and whole‐field synchronised Ca2+ flashes in RMA and increased the frequency of Ca2+ flashes in myogenically active RCA. Furthermore, in RMA, the Gβγ pathway linked NPY to VSM depolarization and generation of action potential‐like spikes associated with intense vasoconstriction. This depolarization activated L‐type voltage‐gated Ca2+ channels, as nifedipine abolished NPY‐mediated vasoconstriction.Conclusions and ImplicationsThese data suggest that the Gβγ subunit, which dissociates upon Y1 receptor activation, initiates VSM membrane depolarization and Ca2+ mobilisation to cause vasoconstriction. This model may help explain the development of microvascular vasospasm during raised sympathetic nerve activity.

Saliva steroid assay is an upcoming area of research, with much potential for growth and progress. Expensive, varying results with commercial kits and the disadvantages of radioimmunoassay have forced researchers to develop their own system of enzyme immunoassay (EIA). A modification from our established EIA system was used to develop a saliva cortisol (F) assay system. The system sensitivity (>90pg/mL) was checked by various experiments, including comparison of data with a commercial kit obtained from Salimetrics. The assay system was employed to investigate the saliva F level in a young Taiwanese population, and compared with the total and free serum levels of F.