Microinfusion of bombesin into the hypothalamic paraventricular nucleus produces hypothermia in the insulin-pretreated rat

Hypothalamus, anterior pituitary and adrenal gland involvement in the activation of adrenocorticotropin and corticosterone secretion by gastrin-releasing peptide

This study was designed to investigate the contribution of the hypothalamus, anterior pituitary and adrenal gland in the increase of adrenocorticotropin (ACTH) and corticosterone secretion induced by gastrin-releasing peptide (GRP) on in vitro isolated hypothalamus, pituitary and adrenal gland. Furthermore, we have examined in dispersed anterior pituitary cells whether the ACTH release induced by GRP is a Ca2+-dependent process. Moderate concentrations of GRP (1 and 10 nM) were able to increase the release of corticotropin-releasing factor (CRF)-like material in the medium of isolated hypothalami, whereas higher concentrations (100 and 1000 nM) were needed to elevate ACTH and corticosterone secretion in pituitary and adrenal quarters, respectively. The competitive and specific GRP receptor antagonist (Leu13-psi-CH2NH-Leu14) bombesin (10, 100 and 1000 nM) was without effect on basal secretion of CRF-like material, ACTH and corticosterone in isolated hypothalami, pituitary and adrenal quarters respectively. However, this antagonist (100 nM) completely blocked the stimulatory effects of GRP (100 nM) on bioactive CRF, ACTH and corticosterone release. In addition, in dispersed anterior pituitary cells which medium contained Ca2+ (1.5 mM), GRP stimulated the secretion of ACTH, but was without effect when the concentration of Ca2+ in the medium was lower (200 nM). These results suggest that: (1) the hypothalamus, anterior pituitary and adrenal gland seem to contribute to the elevation of ACTH and corticosterone secretion induced by GRP by a mechanism mediated through GRP receptors and (2) the stimulation of ACTH by GRP in the anterior pituitary appears to be dependent upon the presence of physiological concentrations of extracellular Ca2+.

Role of corticotropin-releasing hormone in gastrin-releasing peptide-mediated regulation of corticotropin and corticosterone secretion in male rats

Gastrin-releasing peptide (GRP) exerts several functions within the hypothalamus and may be involved in the regulation of pituitary hormone secretion. The purpose of this study was to investigate the central effect of GRP on hypothalamic-pituitary-adrenal axis activity in the male rat. Intracerebroventricular (i.c.v.) but not intravenous administration of GRP (1, 10, 100 ng/rat) increased plasma ACTH and corticosterone concentrations in a dose-dependent manner. The highest dose (100 ng/rat) of GRP increased plasma ACTH and corticosterone 4- and 14-fold, respectively. This increase peaked at 30-60 min after i.c.v. injection, decreased gradually and returned to baseline levels 240 min after GRP administration. The i. c.v. administration of (Leu13-psi-CH2NH-Leu14) bombesin, a competitive and specific GRP receptor antagonist, had no effect on ACTH and corticosterone secretion; however, a dose of 1 microg/rat completely blocked the increase of both hormones induced by GRP (10 ng). By using alpha-helical (9-41) corticotropin-releasing factor (CRF), a competitive antagonist of CRF, the role of CRF on GRP-induced ACTH and corticosterone secretion was also explored. alpha-Helical (9-41) CRF (10 microg/rat) blocked the increase in ACTH and corticosterone secretion induced by GRP (10 ng). The results obtained in this study suggest that GRP increases the secretion of ACTH and corticosterone in the plasma by acting centrally on GRP receptors, and that endogenous GRP receptor ligands do not tonically regulate ACTH and corticosterone secretion. Furthermore, the hypothalamus-pituitary-adrenal-activating effects induced by GRP appear to be mediated, at least in part, by CRF.

Bombesin-induced hypothermia in rats tested at normal ambient temperatures: contribution of the sympathetic nervous system

Rats infused centrally with bombesin become hypothermic at normal ambient temperatures when acutely deprived of food, but not while allowed unrestrained access to food. Ad lib-fed rats, tested at normal ambient temperatures, become hypothermic after receiving intracerebroventricular (ICV) bombesin when they have ventromedial hypothalamic lesions or when administered insulin or 2-deoxy-D-glucose peripherally. All of these conditions have been linked to reductions of sympathetic nervous system activity to brown adipose tissue (BAT), a major thermogenic mechanism of many homeotherms. A between group design was used to examine the effects of ICV bombesin infusions on the response to peripheral injections of a) the sympathetic ganglionic blocker chlorisondamine (2.5 mg/kg, IP) in ad lib-fed rats, b) the nonspecific beta-agonist isoproterenol (30 mg/kg, IP) in food-deprived rats, and c) the combination of isoproterenol and chlorisondamine in ad lib-fed rats. Ad lib-fed rats receiving ICV bombesin (100 ng/5 microliters), in combination with peripheral chlorisondamine injection, became hypothermic 60 min postbombesin administration (-2.84 +/- 0.33 degrees C), while ad lib-fed rats receiving ICV bombesin infusion and peripheral injections of saline did not (-0.08 +/- 0.37 degrees C). Isoproterenol blocked hyperthermia in ad lib-fed rats injected with chlorisondamine and ICV bombesin. Food-derived rats receiving ICV bombesin infusion and peripheral saline injection exhibited hypothermia 60 min postbombesin administration (-2.51 +/- 0.29 degrees C). Peripheral injections of isoproterenol prevented bombesin-induced hypothermia in food-deprived rats. These data suggest that bombesin induces hypothermia at normal ambient temperatures when the sympathetic nervous system drive to BAT cannot be (or is not) activated.

Dissociated feeding and hypothermic effects of neuropeptide Y in the paraventricular and perifornical hypothalamus

The present study investigated the effects of neuropeptide Y (NPY) on food intake and body temperature (Tbo) in free-feeding unrestrained rats following injection into the medial hypothalamic paraventricular nucleus (PVN) or the lateral perifornical hypothalamus (PFH). NPY (78-235 pmol) or saline was infused unilaterally into the PVN or PFH in a volume of 0.4 microliter and simultaneous measures of food intake and Tbo were taken every 30 min for 3 h. Results indicated that NPY evoked changes in eating behavior and Tbo that were dependent upon the site of hypothalamic injection. Although PVN and PFH administration of NPY both increased food intake dose dependently within 30 min of treatment, PFH NPY-injected rats (n = 9) showed a stronger behavioral response compared to rats (n = 9) receiving NPY injections into the PVN. In PVN-treated rats, however, the increased eating was associated with a significant decline in Tbo evident within the first 30-min test interval. A mean maximal decline of 0.92 +/- 0.26 degree C occurred within 90 min of PVN treatment of the highest dose, which produced a reduction in Tbo that was maintained for 2.5 h. In contrast, NPY infusion into the PFH failed to reliably alter Tbo at any of the doses tested. These findings are consistent with evidence that NPY in the PVN and PFH may have distinct functions and suggest that although PFH NPY acts to stimulate a robust and relatively specific ingestive response, PVN NPY may participate in the complex integrative mechanisms responsible for the simultaneous regulation of feeding, thermoregulatory, and metabolic processes.

Food deprivation does not influence body or selection temperature in rats receiving intraventricular bombesin

Bombesin (BBS), a tetradecapeptide, has been found to have potent hypothermic effects when centrally administered. This study was designed to investigate the relationship between food-deprivation and BBS-induced hypothermia in a temperature selection paradigm. Food-deprived and satiated male Sprague-Dawley rats were given intracerebroventricular (ICV) injections of several doses of BBS and control vehicle. Selection temperature data and changes in core body temperature were measured. BBS produced a significant hypothermia and decrease in selection temperatures in all doses but one. No significant differences in body temperature or selection temperatures were found between food-deprived and satiated animals. The results are consistent with the hypothesis that BBS acts centrally to decrease body temperature set point.

Bombesin-induced hypothermia in VMH-lesioned rats

Microinfusion of bombesin into the lateral ventricles (LV) of rats pretreated with insulin or acutely deprived of food has been demonstrated to reduce core body temperature. Lesions of the ventromedial hypothalamus (VMH) have been shown to produce hyperphagia, hyperinsulinemia, and to alter serum metabolic fuels. The present study examines VMH lesions as a permissive event in bombesin-induced hypothermia in rats tested at normal ambient temperature. A between-group design was used to evaluate the effect of microinjections of bombesin (1, 10, 100 ng) into the LV of rats with bilateral VMH lesions or sham lesions. Core body temperature was recorded over a 240-min period. In animals with lesions of the VMH, hypothermia was demonstrated by 30 min after injection of the 10 ng and 100 ng doses; the hypothermia persisted for 120 min. The 1 ng dose had no effect on body temperature in VMH-lesioned animals. Animals that received sham lesions of the VMH did not demonstrate a reduction in core body temperature at the maximum effective dose (100 ng) of bombesin. These results suggest that some event(s) associated with bilateral VMH lesions acts as a permissive factor in the production of bombesin-induced hypothermia at normal ambient temperature.

Bombesin-induced hypothermia and hypophagia are associated with plasma metabolic fuel alterations in the rat

Microinfusion of bombesin into the preoptic area (POA) has previously been shown to reduce core body temperature and feeding in rats that are food-deprived or made hypoglycemic with insulin. The present study determined the metabolic fuel state of rats under these experimental conditions. In addition, changes in plasma metabolic fuels following the microinfusion of bombesin (50 ng/0.25 microliters) into the POA were evaluated. Rats (n = 8) were tested under conditions of food satiation, food deprivation (20 h), and insulin pretreatment (10 U/kg). Prior to peptide infusion, food-deprived rats exhibited the expected elevation in free fatty acids coupled with a small decline in plasma glucose. Insulin treatment resulted in hypoglycemia which persisted for at least 120 min. Following bombesin infusion, free fatty acids and corticosterone levels were elevated in food-sated rats. Food-deprived rats exhibited elevation in plasma glucose, free fatty acids, and corticosterone following peptide infusion. In insulin-treated rats, bombesin attenuated the hypoglycemia observed in controls and increased corticosterone levels. These findings suggest that bombesin-like peptides localized within the POA may participate in the regulation of metabolic fuels.

Destruction of different fiber tracts underlies development of lateral hypothalamic lesion-induced hyperthermia and loss of bombesin-induced hypothermia

The relative roles of lateral hypothalamic cell bodies and fibers of passage were assessed in the development of lesion-induced hyperthermia and bombesin-induced hypothermia. Electrolytic lesions or discrete fiber transections were combined with intracisternal bombesin injection to show that each of these two thermoregulatory effects involves fibers crossing the borders of the lateral hypothalamus; however, the two effects primarily involve fibers crossing different borders. Thus, the hyperthermia and the abolition of bombesin-induced hypothermia which follow lateral hypothalamic damage appear to result from disruption of separate thermoregulatory pathways.

Bombesin produces hypothermia in rats pretreated with 2-deoxy-D-glucose

Previous research has shown that microinfusion of bombesin into the preoptic area (POA) decreases core body temperature in rats that are food-deprived or made hypoglycemic with insulin. The present study employed 2-deoxy-D-glucose, a competitive inhibitor of glycolysis, to further investigate the importance of a reduction in glucose utilization in the production of bombesin-induced hypothermia. Rats (n = 7) were pretreated with 2-DG (0, 25, 50, 100, 200 mg/kg; IP) followed by bombesin (100 ng/1.0 microliters) microinfusions into the POA. The highest dose of 2-DG (200 mg) was also tested in the absence of bombesin as a control. Pretreatment with 2-DG resulted in a dose-related reduction in Tb following bombesin. Injections of 2-DG alone did not significantly alter Tb. The results provide additional evidence that the production of bombesin-induced hypothermia in fasted rats is linked to a reduction in glucose utilization.

Refeeding attenuates bombesin-induced hypothermia in the rat

The tetradecapeptide bombesin is a potent agent in producing hypothermia when injected centrally. Bombesin-induced hypothermia at normal ambient temperature occurs under conditions of food deprivation or insulin-induced hypoglycemia. This experiment examined the effect of refeeding on the duration of bombesin-induced hypothermia. Rats (n = 7) received microinfusions of bombesin (0.1 microgram/1.0 microliter) into the preoptic area under separate conditions of food deprivation (18 h) and insulin pretreatment (10 U/kg, IM). Core body temperature was evaluated over a period of 4 h with or without food available during testing. Hypothermia was observed under all conditions during the first 2 h. Food-deprived and insulin-pretreated rats not permitted access to food remained hypothermic until at least 4 h following bombesin. These results are discussed in terms of the possible role of glucose availability in the production and duration of bombesin-induced hypothermia.