Jean Camus

VIP activation of rat anterior pituitary adenylate cyclase

The brain gut octacosapeptide VIP (vasoactive intestinal peptide) is found in discrete areas in the cerebral cortex, the hypothalamus and the posterior pituitary gland. Specific VIP binding sites are coupled to an adenylate cyclase system in synaptic membranes from guinea pig brain. Besides, the concentration of VIP in the hypothalamo-hypophysial portal vessels is much higher than in the systemic blood. The peptide has however no established function in the hypophysis. These data document the presence in the rat pituitary of functional VIP receptors existing in the form of a VIP-stimulated adenylate cyclase system and suggest that VIP might be a major peptidic activator of rat adenopituitary membrane adenylate cyclase.

Short-term adaptation of pancreatic hydrolases to nutritional and physiological stimuli in adult rats

Abstract o 1. Adult rats, previously maintained on a chow containing 48 p. cent carbohydrates, were fasted 24 h, then refed for 5 days on various diets. The nutritional stimuli were made up either of 4 p. cent corn oil, 67 p. cent of a carbohydrate, and 18 p. cent casein, or of 50 p. cent lipid, 0 p. cent carbohydrates and 18 p. cent casein (w:w). Other rats were simply starved for 3 or 6 days, and a group was diabetic after 7 days on chow, following alloxan administration. 2. The opposite regulations of α-amylase and lipase were striking. The specific activities of both hydrolases tripled within 5 days in the presence of their best inducers (starch and corn oil respectively). The specific activity of the second enzyme decreased simultaneously to one third of its initial value. These variations were reversible. 3. The specific activity of amylase on 67 p. cent starch, glucose, fructose or sucrose did not exceed that on the 48 p. cent carbohydrate chow. The induction by galactose and lactose was mediocre. Amylase decreased sharply during fasting and in diabetic rats. The enzyme was always depressed on fat-diets, but somewhat less so on tricaprylin. 4. When compared to control values on chow, several circumstances favored lipase induction. The specific activity of lipase in the pancreas doubled in diabetic rats. The increase on 67 p. cent galactose was probably due to reduced glucose tolerance. Diets rich in starch, fructose and sucrose also increased lipase. All 50 p. cent fat diets stimulated lipase. Triolein, and various oils (olive, corn, sunflower, walnut and lineseed oils) yielded results twice as good as those with more saturated fats (tricaprylin, tristearin and lard). 5. The activities estimated in the small intestine partially reflected inductions.

Cyclic nucleotide-dependent protein kinases of the rat pancreas

Abstract A cyclic GMP-dependent protein kinase, which catalyzes the phosphorylation of histones and protamine by ATP, was present together with a cyclic AMP-dependent protein kinase and a readily active protein kinase in the rat pancreas. These three protein kinases were separated by chromatography on DEAE-cellulose. The cyclic GMP-dependent protein kinase was relatively cationic and fragile. Upon activation by cyclic GMP, this kinase dissociated into a light catalytic subunit and a somewhat heavier cyclic GMP binding subunit. A crude 27,000 × g pancreas supernatant had two apparent Ka values for cyclic GMP of 2.10−8 M and 3.10−7 M. The possible relationships between protein kinases and enzyme secretion are discussed.

The influence of detergents and trypsin on the stimulation of amylase secretion by either pancreozymin or sodium fluoride in the perfused rat pancreas

Abstract (1) Rat pancreas fragments were perfused for 2hr with Krebs-Ringer bicarbonate buffer enriched with 10 mM glucose and Trasylol (500 UIK/ml). Amylase output was estimated at 5-min intervals on successive samples of the effluent. (2) Pancreozymin at a concentration of 7.10−9 M doubled amylase output when introduced after 1 hr of preincubation. Administration of 10 mM NaF promoted a biphasic effect. The initial and transient hypersecretory peak was followed by a second and more prolonged period of hypersecretion. It is assumed that the primary component of the biphasic response was due to hyperosmolarity, and it is tentatively suggested that the secondary response to NaF was the result of variations in the phosphorylation of membrane proteins. (3) Paired tissue fragments were pre-exposed for 30 min to digitonin, sodium dodecylsulfate, Triton X-100, or bovine trypsin (the proteolytic enzyme in the absence of Trasylol). The basal output of amylase rose with increasing detergent concentrations (from 100 to 500 μg/ml but not after trypsin pretreatment. The four agents were equally effective in reducing the sensitivity to pancreozymin. They did not impair the initial osmotic response to NaF, but did curtail the prolonged second NaF hypersecretory effect. Digitonin and dodecylsulfate were less effective in this respect than either Triton X-100 or trypsin though being equally detrimental to pancreozymin action. (4) These observations suggest that the regulation in vitro of secretion by pancreozymin and NaF in intact acinar cells of the rat pancreas involves two distinct loci of a membrane-lipoprotein complex.

Characterization of muscarinic receptors in human pancreatic membranes.

Crude membranes (27,000 × g pellets) from three normal human pancreata were prepared. Muscarinic receptors were investigated by the ability of three antagonists (atropine, pirenzepine, and AF-DX 116) and three agonists (carbamylcholine, oxotremorine, and pilocarpine) to inhibit[3H]NMS binding. These receptors showed for pirenzepine and AF-DX 116 a M2β specificity, typical of secretory glands and smooth muscle, that was comparable to that of rat pancreatic membranes, i.e., a low affinity for the two antagonists (Kiof 0.4 and 0.2 μM, respectively). In addition, these receptors were predominantly in a low affinity state for the agonist carbamylcholine (Ki of 100 μM).