Neonatal capsaicin causes compensatory adjustments to energy homeostasis in rats

Abstract

Several mechanisms involved in ingestive behavior and neuroendocrine activity rely on vagal afferent neuronal signaling. Seemingly contradictory to this idea are observations that vagal afferent neuronal ablation by neonatal capsaicin (CAP) treatment has relatively small effects on glucose homeostasis and long-term regulation of energy balance. It may be proposed that humoral endocrine factors and/or their sensitivities compensate for the loss of vagal afferent information, particularly when subjects face disturbances in ambient fuel levels. Therefore, male adult rats neonatally treated with CAP or with the vehicle (VEH) underwent intravenous glucose tolerance tests (IVGTTs) during which blood fuel levels, and circulating adipose, pancreatic, and adrenal hormones were assessed. CAP rats displayed similar hyperglycemia as VEH rats, but with markedly reduced plasma insulin and corticosterone responses. These results indicate that CAP rats have increased insulin sensitivity during hyperglycemic episodes, and lower plasma levels of corticosterone in CAP rats relative to VEH rats could underlie this effect. After the IVGTT, CAP rats had increased plasma adiponectin and reduced plasma resistin levels, and these alterations in adipose hormones might be relevant for post-ingestive metabolic processes. In a second experiment, anorexigenic efficacies of cholecystokinin and leptin were assessed. While VEH rats, but not CAP rats, responded with reduced food intake to i.p. injected cholecystokinin, only CAP rats responded to i.v. infused leptin with a reduction in food intake. It is concluded that reduced HPA axis activity and/or increased leptin signaling could underlie compensations in fuel handling and energy balance following CAP treatment.

The passive coping Roman Low Avoidance rat, a non-obese rat model for insulin resistance

“…The pro-active RHA rat revealed no signs of adiposity or insulin resistance. In fact, the glucose and insulin profiles in RHA rats were remarkably similar to those that were found in numerous previous studies in Wistar rats in our laboratory throughout the years [21,23,24]. Taken together this…”

TRP Channels as Therapeutic Targets in Diabetes and Obesity

“…On the other hand, adult male rats, which were neonatally treated with capsaicin, did not differ in body weight, basal plasma leptin, or fasting leptin, insulin, adiponectin, and corticosterone levels [ 86 ]. Glucose levels following intravenous glucose tolerance tests were similar in the capsaicin-treated and vehicle-treated rats [ 86 ].…”

“…On the other hand, adult male rats, which were neonatally treated with capsaicin, did not differ in body weight, basal plasma leptin, or fasting leptin, insulin, adiponectin, and corticosterone levels [ 86 ]. Glucose levels following intravenous glucose tolerance tests were similar in the capsaicin-treated and vehicle-treated rats [ 86 ]. However, the capsaicin-treated rats displayed reduced plasma insulin and corticosterone responses, indicating increased insulin sensitivity and lower plasma corticosterone levels [ 86 ].…”

“…Glucose levels following intravenous glucose tolerance tests were similar in the capsaicin-treated and vehicle-treated rats [ 86 ]. However, the capsaicin-treated rats displayed reduced plasma insulin and corticosterone responses, indicating increased insulin sensitivity and lower plasma corticosterone levels [ 86 ]. The increased insulin sensitivity was also supported by euglycemic hyperinsulinemic clamp studies [ 87 ].…”

Proposal open for discussion: defining agreed diagnostic procedures in experimental diabetes research

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