Noboru Yanaihara

Galanin stimulates growth hormone (GH) secretion via GH-releasing factor (GRF) in conscious rats

The possibility of a role of hypothalamic growth hormone (GH)-releasing factor (GRF) in GH secretion induced by centrally administered galanin was investigated in freely moving male rats. Intracerebroventricular (i.c.v.) injection of synthetic galanin (0.4 or 2 micrograms/rat) elicited a dose-related increase in plasma GH in these conscious rats. Pretreatment with rabbit antiserum specific for rat GRF significantly inhibited the plasma GH increase induced by i.c.v. injection of galanin (2 micrograms/rat). These findings suggest that galanin-induced GH secretion in the rat is mediated at least in part by hypothalamic GRF.

Existence of Met-enkephalin-Arg6-Gly7-Leu8 with Met-enkephalin, Leu-enkephalin and Met-enkephalin-Arg6-Phe7 in the brain of guinea pig, rat and golden hamster

Abstract High performance liquid chromatography (HPLC) coupled with specific radioimmunoassays for methionine-enkephalin-Arg6-Gly7-Leu8 (Met-E-Arg6-Gly7-Leu8), methionine-enkephalin (Met-E), leucine-enkephalin (Leu-E) and methionine-enkephalin-Arg6-Phe7 (Met-E-Arg6-Phe7) has demonstrated that Met-E-Arg6-Gly7-Leu8 exists together with Met-E, Leu-E and Met-E-Arg6-Phe7 in the brain of guinea pig, rat and golden hamster. The content of Met-E-Arg6-Gly7-Leu8 was comparable to those of Leu-E and Met-E-Arg6-Phe7, whereas that of Met-E was the highest among the four opioid peptides. These results are compatible with the recent studies on the nucleotide sequence of cloned cDNA for preproenkephalin from bovine adrenal medulla, which reveal that this precursor molecule contains four copies of Met-E and one copy each of Leu-E, Met-E-Arg6-Phe7 and Met-E-Arg6-Gly7-Leu8. The co-existence of Met-E-Arg6-Gly7-Leu8 with Met-E, Leu-E and Met-E-Arg6-Phe7 suggests that their biosynthetic pathway in the brain is similar to that in the adrenal medulla.

Effects of VIP, TRH, GABA and dopamine on prolactin release from superfused rat anterior pituitary cells

Effects of VIP, TRH, dopamine and GABA on the secretion of prolactin (PRL) from rat pituitary cells were studied in vitro with a sensitive superfusion method. Dispersed anterior pituitary cells were placed on a Sephadex G-25 column and continuously eluted with KRBG buffer. Infusion of TRH (10(-11) - 10(-8)M) and VIP (10(-9) - 10(-6)M) resulted in a dose-related increase in PRL release. LHRH (10(-8) - 10(-5)M) had no effect on PRL release. On the other hand, infusion of dopamine (10(-9) - 10(-6)M) and GABA (10(-8) - 10(-4)M) suppressed not only the basal PRL release from dispersed pituitary cells but also the PRL response to TRH and VIP. The potency of TRH to stimulate PRL release is greater than that of VIP, and the potency of dopamine to inhibit PRL secretion is stronger than that of GABA on a molar basis. These results indicate that TRH and VIP have a stimulating role whereas dopamine and GABA have an inhibitory role in the regulation of PRL secretion at the pituitary level in the rat.

A novel opioid peptide, leumorphin, acts as an agonist at the κ opiate receptor

Abstract The primary structure of the common precursor of porcine β-neo-endorphin and dynorphin (preproenkephalin B) has shown the existence of a third leucine-enkephalin (leu-enkephalin) sequence with a C-terminal extension of 24 amino acids. This nonacosapeptide, named leumorphin, was approximately 70 times more potent than leuenkephalin in inhibiting the contraction of the myenteric plexus-longitudinal muscle preparation of the guinea pig ileum. This action of leumorphin, like those of β-neo-endorphin and dynorphin, was antagonized less effectively by naloxone than that of leuenkephalin, but more effectively by Mr2266, an antagonist relatively specific for the κ type opiate receptor. The inhibitory action of leumorphin or β-neo-endorphin on the contraction of the guinea pig ileum muscle strip was reduced in a dose-dependent manner by pretreatment with dynorphin and vice versa . Leumorphin as well as β-neo-endorphin and dynorphin inhibits the contraction of the rabbit vas deferens which is known to have only the κ type opiate receptor. This action was also effectively antagonized by Mr2266. It is concluded that leumorphin has potent opioid activity and acts at the κ receptor, like other opioid peptides derived from preproenkephalin B.

Involvement of Hypothalamic Vasoactive Intestinal Polypeptide (VIP) in Prolactin Secretion Induced by Serotonin in Rats

Abstract To study the possible involvement of hypothalamic vasoactive intestinal polypeptide (VIP) in regulating the secretion of prolactin (PRL), the effect of anti-VIP rabbit serum on serotonin (5-HT)-induced PRL release was examined in urethane-anesthetized male rats. Anti-VIP serum (AVS) or normal rabbit serum (NRS) was infused into a single hypophysial portal vessel of the rat for 40 min at a rate of 2 μl/min with the aid of a fine glass cannula and 5-HT was injected into a lateral ventricle 10 min after the start of the infusion. Intraventricular injection of 5-HT (10 μg/rat) caused an increase in plasma PRL levels in control animals infused with NRS and 5-HT-induced PRL release was blunted in animals infused with AVS (mean±SE peak plasma PRL: 118.9±19.8 ng/ml vs 54.7±16.2 ng/ml, p<0.05). These findings suggest that the secretion of PRL induced by 5-HT is mediated, at least in part, by hypothalamic VIP release into the hypophysial portal blood in the rat.

Inhibition of Prolactin Secretion by Gastrin Releasing Peptide (GRP)in the Rat

Abstract Synthetic gastrin releasing peptide (GRP) injected intraventricularly (1μg/rat), but not intravenously, suppressed rat prolactin (PRL) release induced by a Met-enkephalin analog, FK33-824 (10 μg/100 g body wt., iv). GRP also blunted PRL release induced by a dopamine antagonist, domperidone(l μg/100 g body wt., iv). In contrast, GRP did not suppress elevated plasma PRL levels sustained by a large dose of domperidone (10μg/100 g body wt., iv). GRP (10-5M) had no effect on PRL release from super fused pituitary cells in vitro. These results suggest that GRP inhibits PRL secretion in the rat by acting through the brain to stimulate the dopaminergic mechanism

Parallel distribution of methionine-enkephalin-arg6-gly7-leu8 with methionine-enkephalin, leucine-enkephalin and methionine-enkephalin-arg6-phe7 in human and bovine brains

Using specific radioimmunoassays(RIAs) for methionine-enkephalin(Met-Enk), leucine-enkephalin(Leu-Enk), methionine-enkephalin-Arg6-Gly7-Leu8 (Met-Enk-Arg-Gly-Leu) and methionine-enkephalin-Arg6-Phe7 (Met-Enk-Arg-Phe), we studied the regional distribution of these opioid peptides in human and bovine brains. Met-Enk-Arg-Gly-Leu was distributed in parallel with Met-Enk, Leu-Enk and Met-Enk-Arg-Phe in human and bovine brains. The ratios of molar concentrations of these peptides are almost constant in various regions of human and bovine brains and similar to the ratio of these peptides contained in preproenkephalin A. Gel exclusion chromatography and HPLC coupled with respective RIAs showed the existence of authentic peptides without any detectable high molecular weight forms. These results indicate the parallel distribution of Met-Enk-Arg-Gly-Leu with Met-Enk, Leu-Enk and Met-Enk-Arg-Phe in various regions of human and bovine brains and further suggest that these opioid peptides are derived from the same precursor as that in the adrenal medulla and that the processing of preproenkephalin A is almost complete in human and bovine brains.

Comparison of the action of putative endogenous κ-agonists, leumorphin and rimorphin in vitro

Abstract Leumorphin and rimorphin (dynorphin B) were nearly equipotent in inhibiting the contraction of the myenteric plexus-longitudinal muscle preparation of the guinea pig ileum and the rabbit vas deferens. Leumorphin had long duration of action in vitro after wash-out, whereas the duration of action of rimorphin was relatively shorter. These action of leumorphin and rimophin were antagonized less effectively by naloxone than by Mr2266, an antagonist relatively specific for the κ-receptor. Rimorphin as well as leumorphin inhibits the contraction of the rabbit vas deferens which contains soley κ- receptors. It is concluded that leumorphin and rimorphin have equipotent opioid activity and act at the κ-receptor, like other opioid peptides derived from preproenkephalin B.

Met-enkephalin-Arg6-Gly7-Leu8 exists together with Met-enkephalin-Arg6-Phe7, Met-enkephalin and Leu-enkephalin in human stomach.

Studies on the nucleotide sequence of cloned DNA complementary to mRNA for preproenkephalin A from adrenal medulla and human pheochromocytoma have revealed that this precursor contains 4 copies of methionine-enkephalin(Met-Enk) and one copy each of leu-enkephalin (Leu-Enk), methionine-enkephalin-Arg6-Gly7-Leu8(Met-Enk-Arg6-Gly7-Leu8) and methionine-enkephalin-Arg6-Phe7(Met-Enk-Arg6-Phe7). We have demonstrated the existence of Met-Enk-Arg6-Gly7-Leu8 together with Met-Enk, Leu-Enk and Met-Enk-Arg6-Phe7 in human gastric antrum, using high performance liquid chromatography(HPLC) coupled with radioimmunoassays for these opioid peptides. The ratio of molar concentrations of these peptides in human gastric antrum is almost equal to the ratio of these peptides contained in preproenkephalin A. Furthermore, gel filtration studies on Sephadex G-50 showed that most of immunoreactivities of these peptides were eluted at the elution position of each synthetic peptide without any detectable immunoreactivities at high molecular weight positions. In addition, most of immunoreactivities of these four opioid peptides were detected in the muscular layer of the gastric antrum. These results indicate the presence of Met-Enk-Arg6-Gly7-Leu8 together with Met-Enk, Leu-Enk, and Met-Enk-Arg6-Phe7 in human gastric antrum and further suggest that these opioid peptides are derived from the same precursor as preproenkephalin A in the adrenal medulla and the processing of preproenkephalin A is almost completed in the human stomach.

Effects of naloxone on basal and vagus nerve-induced secretions of GRP, gastrin, and somatostatin from the isolated perfused rat stomach

The effects of naloxone, an opiate antagonist, on basal and vagus nerve-induced secretions of GRP, gastrin, and somatostatin were examined using the isolated perfused rat stomach prepared with vagal innervation. Naloxone (10(-6) M) significantly inhibited basal somatostatin secretion in the presence and absence of atropine and of hexamethonium, whereas basal GRP and gastrin secretion was not affected by naloxone. Electrical stimulation (10 Hz, lms duration, 10V) of the distal end of the subdiaphragmatic vagal trunks elicited a significant increase in both GRP and gastrin but a decrease in somatostatin. Naloxone (10(-6) M) failed to affect these responses in the presence or absence of atropine. On the other hand, when hexamethonium was infused, naloxone significantly inhibited both the GRP and gastrin responses to electrical vagal stimulation. Somatostatin secretion was unchanged by vagal stimulation during the infusion of hexamethonium with or without naloxone. These findings suggest that basal somatostatin secretion is under the control of an opiate neuron and that opioid peptides might be involved in vagal regulation of GRP and gastrin secretion.