Preferential release of oxytocin in response to vasoactive intestinal polypeptide in rats

Vasoactive intestinal polypeptide (VIP) was infused into the aorta of pentobarbitone-anesthetized rats (n = 12) in stepwise increasing doses of 0.001 to 10 micrograms/rat at rates varying from 0.3 pmol/min/kg to 3000 pmol/min/kg over 3 min. Blood was withdrawn from the vena cava inferior for the measurement of oxytocin (OT) and vasopressin (AVP) by RIA. The loss of blood was compensated for by infusion of isotonic saline (0.9% NaCl with 0.5% human serum albumin). Control rats received this solution only (n = 11). VIP infusions resulted in a dose-dependent increase in plasma OT which was significantly greater than the slight rise observed in the controls. The difference from controls was significant at infusion rates of 3 pmol/min/kg and more. Plasma AVP, on the other hand, did not rise in response to VIP infusions until the infusion rate was increased to 300 and 3000 pmol/min/kg. At these infusion rates, the increments in AVP were much smaller than those of OT, the levels during the highest infusion rates rising to 8.6 +/- 2.8 and 27.2 +/- 4.8 microU/ml, respectively (log normal means). The preferential release of OT in response to exogenous VIP in rats differs from the response in cats where intracarotid administration of VIP resulted in the release of proportionately more AVP than OT. Immunoreactive VIP is found in the hypothalamo-neurohypophyseal system of rats in close proximity of some of the magnocellular neurons as well as within the nerve terminals. This, together with our data, suggests that endogenous VIP may participate in the release mechanism for OT in rats.     

Atrial natriuretic peptide detected by immunocytochemistry in peripheral organs of Tupaia belangeri

ANP (atrial natriuretic peptide), a peptide found in granules of mammalian atrial cardiac myocytes, has been shown to be active in regulation of blood pressure and body water homeostasis. The existence of ANP in atrium, pituitary, adrenal gland, and kidney of the rat had been immunocytochemically demonstrated with an antibody against rat ANP (102-126). We used the same antibody in immunocytochemical studies for the detection of ANP in peripheral organs of the tree shrew (Tupaia belangeri). The antibody stained granules in myocytes of cardiac atria which indicated that it reacted with tree shrew ANP. In contrast to the rat, no immunoreactive cells were found in pituitaries and adrenal glands. However, in the kidneys distal tubules in outer medulla and cortex were labeled. Ascending limbs of distal tubules were intensely stained when either the peroxidase-antiperoxidase (PAP) or the indirect immunofluorescence method were used. Collecting ducts and convoluted distal tubules in the outer cortex showed a granular type of staining when the immunofluorescence method was used. These data indicate that ANP is present in epithelial cells of distal tubules and collecting ducts, where it may be involved in the regulation of renal salt excretion.     

Immuno-photoaffinity labeling of the D2-dopamine receptor

Azido-haloperidol was synthesized and applied as a photoaffinity ligand for the D2-dopamine receptor. In bovine striatal membranes, azido-haloperidol bound reversibly to the receptor (KD = 15 nM), and when exposed to light, it bound to the receptor irreversibly. This irreversible inactivation was prevented by the dopaminergic agonist N-propylnorapomorphine or the dopaminergic antagonists haloperidol and (+)-butaclamol. The photoaffinity labeled D2-receptor was probed with anti-haloperidol antibodies following gel electrophoresis and transfer to nitrocellulose. A major polypeptide of 94 kDa reacted with the anti-haloperidol antibodies. This polypeptide band was not observed when the photoaffinity labeling was performed in the presence of (+)-butaclamol or spiperone.     

Purification and partial-characterization of a protease inhibitor from Drosophila melanogaster

A protein from Drosophila melanogaster which inhibits bovine alpha-chymotrypsin activity was purified using an extensive extraction procedure. SP-Sephadex column chromatography and affinity column chromatography. The inhibitor has an estimated molecular weight of approx. 12 000 and is extremely pH and heat stable. It did not exhibit any inhibitory activity against trypsin from numerous sources nor mosquito larval chymotrypsin but did inhibit adult mosquito chymotrypsin. Chymotrypsin-like activity has not been found in Drosophila and therefore the function of the inhibitor is unknown. Preliminary work indicates that it effectively inhibits cathepsin D activity from a nematode parasite and rabbit liver.