摘要:

This study examined whether the medial preoptic area (MPOA) is a site which mediates the inhibitory effects of norepinephrine (NE) on pulsatile luteinizing hormone (LH) secretion in ovariectomized rats. Animals were bled continuously at a rate of 50 µl whole blood/7 min for 2 h prior to push-pull perfusion in the MPOA, and during a 2–3 h period of perfusion of the MPOA (20 µl/min) with artificial CSF, or 2 or 20 pg NE/min. In another group of rats LH levels were only determined during a 2–3 h period of MPOA perfusion with CSF. Pulsatile LH release was not affected by push-pull perfusion with CSF when a comparison was made to preperfusion LH values in the same rats. Moreover, LH levels obtained from rats only bled during MPOA perfusion with CSF were not different from LH values obtained during the preperfusion periods in the other groups. However, push-pull perfusion of the MPOA with 2 or 20 pg NE/min significantly suppressed mean LH levels by causing a 35–45% reduction in pulse frequency. No decrease occurred in LH pulse amplitude. Therefore, these studies demonstrate that NE acting at the level of the MPOA can suppress pulsatile LH release solely by decreasing LH pulse fr

ISSN:0028-3835    

DOI:10.1159/000124097

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

Surgical removal of the neurointermediate lobe of the pituitary gland (-X) in the rat resulted in two abnormalities in ACTH secretion: (1) plasma ACTH and corticosterone levels were elevated in the morning and over a 24-hour period compared with levels in control (-C) rats, and (2) although -X and -C rats had acute increases in plasma ACTH and corticosterone of equal magnitude after interoceptive stimuli (hemorrhage, surgery), -X rats demonstrated markedly smaller elevations in plasma levels of these hormones after neurotropic stimuli (noise, novel environment). This subnormal adrenocortical response of -X rats was not due to an impairment in perception of a neurotropic stimulus; these rats had normal latencies to paw licking and to jumping off a heated surface, yet smaller increases in plasma corticosterone after the stimulus. The impairment in ACTH response was not related to stimulus intensity, as -X and -C rats had equal ACTH and corticosterone secretion during both low and high levels of insulin-induced hypoglycemia. -X rats demonstrated a significant elevation in daily water intake, although hematocrit, plasma Na +, K+, osmolality and protein were normal. Significant diurnal rhythms in plasma corticosterone levels and in water intake were maintained as well. The elevated morning plasma ACTH levels, the blunted hormone increases after noise, and the increase in water intake persisted in -X rats 2 months after surgery. These data indicate that removal of the results in (1) chronic elevations in basal ACTH and corticosterone secretion, and (2) chronic impairment in adrenocortical responses to neurotropic stimuli, but not to interoceptive stimuli. The deficit is not due to impaired perceptual capacity nor to the intensity of the stimulus.

ISSN:0028-3835    

DOI:10.1159/000124098

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

We studied the responses of the hypothalamo-neurohypophysial system to intravenous infusions of 18% saline, 25% mannitol and a combination of 15% mannitol and 1.35% saline in conscious, chronically catheterized Long-Evans rats. Infusions of 18% saline and 25% mannitol produced similar increases in plasma osmolality (Posm) and plasma vasopressin-associated neurophysin concentration ([VP-RNP]). As expected, plasma sodium concentration ([Na+]) for the 18% saline-treated animals was significantly elevated while that for the 25% mannitol-treated animals was significantly reduced. Mannitol infusion caused a significantly greater loss of body weight. The slopes of the relationship between Δ[VP-RNP] and ΔPosm were almost identical for the two groups. Infusion of a combination of 15% mannitol and 1.35% saline produced a rise in Posm comparable to that observed for the other two infusion regimens, but caused smaller increases in [VP-RNP], the slope of the relationship between Δ[VP-RNP] and ΔPosm being about half of those for the infusion with 18% saline or 25% mannitol. This combination also maintained [Na+] close to normal levels and in these animals there was a loss of body weight that was significantly smaller than that for those rats receiving 25% mannitol. The results of this study imply that factors other than osmoreceptors and/or sodium receptors are involved in causing a release of neurohypophysial principles during acute infusion of hypertonic soluti

ISSN:0028-3835    

DOI:10.1159/000124099

出版商:S. Karger AG    

年代:1985

数据来源: Karger