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The Endocrine Profile of Synthetic Secretin-Glucagon Family PeDtides and Some Analogues in the Eat. V. A. LANCE, W. A. MURPHY, J. SUEIRAS-DIAZ, and D. H. COY. (Tulane Medical Center, Department of Medicine, 1430 Tulane Avenue, New Orleans, Louisiana 70112).

Secretin, glucagon, VIP, GIP, PHI and GH-RH (1-29) were tested alone and in various combinations on growth hormone (GH), prolactin, insulin and glucagon secre- tion in the fasted rat. Each of the peptides was also tested for its effect on blood glucose in the fed rat. Secretin, GIP, glucagon and VIP inhibited basal and GH-RH-stimulated GH secretion. In most instances the effects were biphasic, showing an antagonist effect at a low dose and an agonist effect at a high dose. PHI caused a slight stimulation of GH secretion. PHI and GIP caused significant hypoglycemia, and GH-RH and VIP a slight hypoglycemia. Secretin caused a slight hyperglycemia. All of the glucagon analogues synthesized, with the exception of D-Phe-4-glucagon, exhibited reduced agonist activity. D-Phe-4-glucagon, however, was six times more potent than native glucagon in stimulating glucose secretion. Four analogues of GH-RH with amino acid substitutions in the l, 4, or 6 position were either inactive or weak agonists. These results indicate that the six N-terminal residues are im- portant determinants of biological activity. The considerable amino acid sequence overlap in this group of peptides and the overlap in biological activities suggest that interaction at the receptor site may have important consequences in vivo. Supported by NIH grant AM-30167.

Characterization and Localization of Vasoactive Intestinal Peptide (Vl~ Receptors in Rat Lung. P. LEROUX, A. FOURNIER, S. ST-PIERRE and G. PELLETIER (MRC Group in Molecular Endocrinology, CHUL, Quebec and Department of Pharmacology, CHUS, Sherbrooke, Canada).

Immunocytochemical studies have shown the existence of a VIPergic innervation in the respiratory tract of the rat. Immunoreactlve nerve fibers are located in the main bronchi, but not in the alveolar regions. Recently, Rebberecht et al. (Biochem. Biophys. b~ta 678: 76, 1981) have demonstrated VlP-dependent adenylate cyclase activity in rat lung membranes. Thus it appeared of interest to character- ize VIP receptors and to study their localization in the rat lung. [1251]VIP binding to lung homogenates was inhibited by synthetic VIP, [Val ~] secretin, secretin and 7-27 secretin with DEbo values of 1.62. 13, 172 x IO-9M and > 0.i x 10-3M, respectively. The relative affinity of [Val 5] secretin and 7-27 secretin indicated that [1251]-VIP binds to specific VIP receptors. Kinetic studies showed two sites of binding, a site of high affinity with a K d value of 0.32 ± 0.09 nM and Bmax of 88.7 ± 28.6 fmoles/mg protein and a low affinity site with a K D value of 23.0 ± 2.9 nM and a high capacity (584 fmole/mg protein). The localization of VIP receptors was performed by radloautography both "in vlvo" after intravenous injection of 0.63 ~g of 1251-VIP (specific radioactivity 300 Ci/mmol) and "in vitro" by the direct application of the radiolabelled peptlde to cryostat sections of un- fixed lung tissue. After injection of label, silver grains were only detected over alveoll. Electron microscopy indicated that radioactivity was mostly associated with alveolar capillaries. "In vitro" localization showed specific binding not only to alveoll but also to bronchi. These studies suggest that VIP could exert some physiological effects at the level of several structures and that the peptide could gain access to alveoll via the general circulation.