Studies on peptides. CXXXIII. Synthesis and biological activity of galanin, a novel porcine intestinal polypeptide

Effect of galanin on plasma glucose, insulin and pancreatic glucagon in dogs

The effect of synthetic galanin on plasma glucose, insulin and pancreatic glucagon levels in dogs was studied. Infusion of galanin caused a rapid, reversible and dose-dependent reduction in basal insulin level. A maximal increase in blood glucose level accompanying the insulin decrease was observed when galanin was administered at a dose of 4 micrograms/kg per h. Pancreatic glucagon levels showed little change compared with basal secretion. These results indicate that galanin is involved in the regulation of glucose through control of insulin secretion.

Oxytocin modulates the effects of galanin in carrageenan-induced hyperalgesia in rats

In the present study we have investigated the effects of galanin and/or oxytocin on carrageenan-induced hyperalgesia, the relationship between oxytocin and galanin-containing nerve fibers in the spinal cord and the influence of galanin on oxytocin secretion. Galanin (1 microgram) given intrathecally (i.t.) decreased significantly the mechanical nociceptive threshold of the carrageenan-treated hindpaw, with no significant effect on thermal nociception. The decrease in the mechanonociceptive threshold exerted by galanin was modulated by oxytocin (1 microgram, i.t.) administered simultaneously. There was a close relationship between galanin- and oxytocin-immunoreactive fibers in the dorsal horn of the thoracic spinal cord, although there was no evidence for colocalization. Galanin 0.1 and 1 microgram given intracerebroventricularly or intraperitoneally significantly decreased the oxytocin level in plasma 60 min after injection. Taken together, these data indicate that galanin may contribute to mechanical hyperalgesia by inhibiting the release of oxytocin from nerve terminals in the spinal cord and that oxytocin may be a potential analgesic agent.

Involvement of substance P in hyperalgesia induced by intrathecal galanin

Previously we have demonstrated that an intrathecal injection of galanin (GAL) decreases the nociceptive threshold for mechanical stimulation without effect on thermal nociceptive responses. The present experiments were conducted to determine whether substance P (SP) would be involved in such a decrease in the nociceptive threshold produced by GAL. An intrathecal injection of anti-SP monoclonal antibody inhibited the nociceptive threshold-decreasing effect of intrathecal GAL (0.1 nmol/rat). This antibody significantly suppressed the contractile action of SP (3 nM) on the longitudinal muscle and that of neurokinin A (3 nM) to a lesser degree. Binding of [125I]Tyr8-SP to this antibody was inhibited by SP in a concentration-dependent manner in the range 0.1-33 nM without suppression by GAL at a concentration of 3300 nM. In addition, an intrathecal injection of the anti-SP monoclonal antibody increased the nociceptive threshold for mechanical stimulation in carrageenin-inflamed rats without effect on thermal nociceptive behaviors. The capsaicin (0.5 microM)-evoked release of immunoreactive SP from dorsal-half slices of the spinal cord was increased by galanin (1 microM, but not 0.1 microM) without effects on basal release. An intrathecal injection of GAL did not produce aversive responses (biting, licking and scratching) at doses of 0.1 and 1 nmol/rat. GAL (0.1 nmol/rat) did not affect biting/licking behaviors evoked by SP (1 nmol/rat), but inhibited SP-evoked scratching behavior. These results suggest that the nociceptive threshold-decreasing action of intrathecal GAL is at least in part mediated by SP, and that GAL may act on primary afferent terminals to increase the release of SP evoked by stimulation.

Intrathecal injections of galanin and its antiserum affect nociceptive response of rat to mechanical, but not thermal, stimuli

To ascertain the involvement of galanin in nociceptive transmission in the spinal dorsal horn, we examined the effects of intrathecal injections of porcine galanin and its antiserum on behavioral nociceptive responses of the rat, using the paw-pressure and paw-radiant heat tests. An intrathecal injection of antiserum against porcine galanin reversed the decreased nociceptive threshold for mechanical, but not thermal, stimulation of the carrageenin-treated hind paw of rat, with no effect on the nociceptive threshold of the non-inflamed hind paw. Rat galanin as well as porcine galanin suppressed the binding of [125I]porcine galanin to the antiserum, a finding suggesting that the antiserum can bind rat galanin. An intrathecal injection of porcine galanin (0.1 and 1 nmol, but not 0.01 nmol) decreased the mechanical nociceptive threshold of the rat hind paw with no effect on thermal nociception. These results suggest that galanin present in the dorsal horn is involved in the facilitation of mechanical, but not thermal, nociceptive transmission.