ABSTRACT
Vasoactive intestinal peptide (VIP), a neuromodulator present in the hypothalamus, plays an important role in the regulation of food intake. Paraventricular nucleus of the hypothalamus (PVN) is involved in ingestive responses and regulates the nitric oxide (NO) pathway. The main objectives of this study were to investigate metabolic changes established after different doses and times of VIP microinjection on the PVN, and the effect of VIP microinjection on the PVN on food intake and the role of NO in this control. In anesthetized rats, increased blood plasma glucose and insulin levels were observed following the doses of 40 and 80 ng/g of body weight. At the dose of 40 ng/g, VIP promoted hyperglycemia and hyperinsulinemia 5, 10, and 30 min after microinjection, and increased free fatty acids and total lipids plasma levels after 5 min, and triglycerides after 10 min. In awake animals, once again, VIP administration increased plasmatic levels of glucose, free fatty acids, corticosterone, and insulin 10 min after the microinjection. Moreover, VIP promoted hypophagia in the morning and night periods, and L-arginine (L-Arg) and monosodium glutamate (MSG) or a combination of both attenuated VIP-induced reduction on food intake. In addition, nitrate concentration in the PVN was decreased after VIP microinjection. Our data show that the PVN participates in the anorexigenic and metabolic effects of VIP, and that VIP-induced hypophagia is likely mediated by reduction of NO.
Subject(s)
Insulins , Paraventricular Hypothalamic Nucleus , Animals , Arginine/metabolism , Arginine/pharmacology , Blood Glucose/metabolism , Corticosterone , Fatty Acids, Nonesterified/metabolism , Fatty Acids, Nonesterified/pharmacology , Insulins/metabolism , Insulins/pharmacology , Neurotransmitter Agents/metabolism , Nitrates/metabolism , Nitric Oxide/metabolism , Rats , Sodium Glutamate/metabolism , Sodium Glutamate/pharmacology , Triglycerides/metabolism , Triglycerides/pharmacology , Vasoactive Intestinal Peptide/metabolism , Vasoactive Intestinal Peptide/pharmacologyABSTRACT
Sex differences related with pain have been studied and evidences suggesting influence of sex steroid hormones on the thresholds of pain. Experimental nociception has been test using formalin as a model of nociceptive stimulus. Association of stress, pain and metabolic and hormonal changes has not been explored. The aim of this study was to compare metabolic and hormonal changes between male rats and female rats in proestrus and estrus cycle after painful stimulus by formalin into the masseter muscle. Male and female Wistar rats (200-250 g b.w.) were submitted to an injection of formalin (F, 1.5%) or saline (S, 9.9%) into the masseter muscle and after 0 (N, control group without injection), 5, 15, 30 or 60 minutes they were decapitate and blood was collected to measure biochemical parameters. Plasma estradiol concentration (pg dL-1) was significantly higher in proestrus (106.3 ï± 4.3, n = 45, p < 0.05) group compared to the estrous group (89.4 ï± 3.5, n = 43). Blood plasma concentration of glucose (mg dL-1) was increased after 5 and 15 minutes of injection of formalin or saline in the animals, but in the estrus group the increase was bigger than in the others. Free fatty acids levels increased in the estrous group after 5, 15 and 30 minutes and also the corticosterone levels and these concentrations were significantly different (p < 0.05) from either male or female animals in proestrus state. The results obtained suggesting that estradiol is related to a sensibility to pain and the estrus stage is related to stress and the estrous cycle has a modulator effect on pain and nociceptive sensibility.
Estudos experimentais têm demonstrado a existência de diferenças sexuais na resposta de dor, e as evidências sugerem a influência de hormônios sexuais na experiência dolorosa. O objetivo deste estudo foi o de comparar as alterações metabólicas e hormonais entre machos e fêmeas em proestro e estro após o estímulo doloroso por formalina no músculo masseter. Ratos machos e fêmeas Wistar (peso: 200-250 g) foram submetidos a uma injeção de formalina (grupo F, 1,5%) ou salina (grupo S, 9,9%) no músculo masseter e depois de 0 (grupo N, controle sem injeção), 5, 15, 30 ou 60 minutos foram decapitados e retirouse o sangue para dosagens bioquímicas. A concentração plasmática de estradiol (pg dL-1) foi significativamente maior no proestro (106,3 ± 4,3, n = 45, p < 0,05) em comparação com o grupo em estro (89,4 ± 3,5, n = 43). A concentração sanguínea de glicose plasmática (mg dL-1) aumentou após 5 e 15 minutos da injeção de formalina ou salina nos animais, mas no grupo estro o esse aumento foi maior. A concentração plasmática de ácidos graxos livres e de corticosterona demonstrou níveis elevados no grupo estro após 5, 15 e 30 minutos apresentando uma diferença significante (p < 0,05) em relação aos animais machos ou fêmeas em proestro. Os valores de glicose, ácidos graxos livres e corticosterona mais elevados nas fêmeas em estro sugerem que a fase do ciclo estral pode estar interferindo na resposta de estresse, podendo estar relacionada com a diminuição na concentração de estradiol.
