Papel dos receptores andrenérgicos da preóptica medial (APM) no controle da salivação induzida pela ativação colinérgica em ratos.
Resumo
The present work had as objective to investigate the participation of the
mechanisms adrenergics of the medial preoptic area (APM) in the salivary secretion
induced for the peripheral colinergic stimulation (pilocarpine injection). Holtzman
rats had been used (280-320 g). A part of the animals suffered electrolytic lesion in
the APM through the ticket from electric chain (1mA x 3x10s), to serve as control,
and another part of the animals was submitted to the same procedures of cerebral
surgery, except that it was not displayed to the electric chain ticket (SHAM). Animals
that suffered the surgery from implant of cannulas guides in the APM for the
injection of adrenergics agonists and antagonists were also used. The saliva was
collected using previously weighted and inserted balls of cotton in the mouth of the
animal that was under anesthesia with quetamina (1mg/mL/kg). Salivation was
induced for intraperitoneal injection (IP) of pilocarpine (1mg/mL/kg). The APM
lesion in such a way reduced peripheral the pilocarpine-induced salivation group that
suffered APM lesion 24 hours before the experiment (APM lesion 340,7 ± 41,1
mg/7min, versus SHAM 428,4 ± 31,6 mg/7min) as much as in the group that suffered
APM lesion 5 days before the experiment (APM lesion 310,2 ± 35,4 mg/7min, versus
SHAM 494,9 ± 35,5 mg/7min). Reduction in the peripheral pilocarpine-induced
salivation was not verified in those animals that had suffered APM lesion 15 days
before the experiment (APM lesion 461,6 ± 81,4 mg/7min, versus SHAM 575,7 ±
34,9 mg/7min). The injection of noradrenaline (80 nmol/0,5µL) in the APM did not
reduce the peripheral pilocarpine-induced salivation (NOR + Pilo 356,0 ± 36,0
mg/7min versus Saline + Pilo 475,0 ± 73,0 mg/7min). This same drug in the dose of
160 nmol/0,5 µL reduced the peripheral pilocarpine-induced salivation (NOR + Pilo
251,0 ± 50,0 mg/7min versus Saline + Pilo 468,0 ± 59,0 mg/7min). The inhibitory
effect of the injection in the APM of noradrenaline (160 nmol/0,5µL) in the
peripheral pilocarpine-induced salivation was not reduced by the previous injection of
the antagonist of adrenoceptors α2, RX-821002 in the dose of 80 nmol/0,5µL (RX +
NOR + Pilo 244,1 ± 29,2 mg/7 min, versus Saline + NOR + Pilo 202,3 ± 34,8 mg/7
min). On the other hand, this same drug injected in the dose of 160 nmol/0,5µL,
partially reverted the inhibitory effect of the injection in the APM of noradrenalina
(160 nmol/0,5µL) in the peripheral pilocarpine-induced salivation (RX + NOR + Pilo
329,9 ± 77,8 mg/7min, versus Saline + NOR + Pilo 148,2 ± 30,3 mg/7min). The RX-
821002 injected in the APM in the dose of 320 nmol/0,5µL, failed in showing the
reversion of the inhibitory effect of the injection in the APM of noradrenaline
(160nmol/0,5µL) in the peripheral pilocarpine-induced salivation (RX + NOR +
261,3 ± 18,9 mg/7min, versus Saline + NOR + Pilo 320,4 ± 30,2 mg/7min). The
antagonist of adrenergics receptors α1, Prazosin, did not reveal efficient, therefore the
inhibitory effect of the injection in the APM of noradrenaline (160 nmol/0,5µL) in the
peripheral pilocarpine-induced salivation was not reduced by the previous injection of
the adrenergic antagonist α1, Prazosin, in the dose of 160 nmol/0,5µL (Prazosin +
NOR + Pilo 223,6 ± 35,8 mg/7min, versus Saline + NOR + Pilo 256,0 ± 58,5
mg/7min). The results show that the noradrenaline injected in the APM reduces the
peripheral pilocarpine-induced salivation and this effect is reduced by the previous
blockade of the receiving adrenergics α2 of the same area, suggesting to the
existence of an adrenergic α2 inhibitory mechanism of the salivation in the APM.