Faculty Bibliography

The release of immunoreactive somatostatin (SRIF) from explants of rat medial basal hypothalamus, which were maintained in culture for 24 h, was quantitated by a sensitive RIA. Validity of the specific SRIF assay has been previously established by chromatographic criteria using gel and high pressure systems and by the demonstration of immunological parallelism. After 24 h of culture in medium containing heat-inactivated fetal calf serum, hypothalamic fragments were incubated in serum-free medium, and the release of immunoreactive SRIF was quantitated. Melatonin at concentrations of 10(--8) and 10(--7) M stimulated SRIF release, and no significant increases were observed at concentrations of 10(--9) M or less or at concentrations of 10(--6) M or greater. Serotonin oxalate at concentrations of 10(--8)--10(--5) M significantly inhibited SRIF release. The serotonin antagonist cyproheptadine at a concentration of 10(--5)M had no effect on basal SRIF release but abolished the inhibitory effect of 10(--7) M serotonin. Finally, when hypothalami were incubated with melatonin and serotonin, each at 10(--7) M, SRIF release was unchanged compared to control values. The results suggest that the brain indoleamines, melatonin and serotonin, may modulate GH secretion by effects on SRIF release at a hypothalamic level

Acetylcholine, at concentrations of 10(-10)--10(-7) M, inhibited the release of immunoreactive somatostatin (SRIF) from rat hypothalamic segments which had been maintained in short term culture for 24 h. Neostigmine (10(-6) M), an anticholinesterase, also inhibited the release of SRIF, whereas atropine (10(-6) M), a muscarinic anticholinergic, had no effect on basal SRIF release but blocked the inhibition caused by acetylcholine (10(-8) M). However, hexamethonium (10(-6) M), a nicotinic antagonist, did not abolish the inhibition induced by acetylcholine. Potassium depolarization (56 mM KCl) caused stimulation of SRIF release, which was dependent on the presence of calcium in the incubation medium. SRIF was measured by a RIA sensitive to 1 pg/tube. Authenticity of immunoreactive SRIF released was suggested by immunological parallelism and chromatographic criteria using gel and high pressure liquid systems. These results suggest that muscarinic cholinergic mechanisms may have a regulatory role modulating the secretion of SRIF and, consequently, GH through actions at a hypothalamic level

An easily performed assay to identify the C3b and Fc receptors on human neutrophils was developed. Salmonella typhimurium were treated with fluorescein and then incubated in nonimmune fresh human serum, which led to C3b fixation via activation of the alternative pathway. Similarly, type II pneumococci were treated with fluorescein and opsonized with type-specific rabbit antiserum. Neutrophils bearing C3b and Fc receptors formed rosettes with the respective bacteria, which were easily readable because of their bright fluorescence. Incubation of neutrophils at 37 degrees C with C3-coated bacteria generated 54 +/ 4% C3b rosettes, whereas neutrophils incubated with immunoglobulin G-coated bacteria yielded 75 +/ 7% rosettes. Incubation at 4 degrees C inhibited the formation of C3b rosettes but not Fc rosettes. Heat inactivation of the fresh human serum at 56 degrees C for 30 min completely inhibited the formation of the C3b rosettes, and addition of heat-aggregated immunoglobulin G to the polymorphonuclear leukocyte blocked the ability of the polymorphonuclear leukocyte to bind immunoglobulin G-coated bacteria. Addition of 1.0 mM N-ethylmaleimide, 0.1 mg of trypsin per ml, 10 mM H2O2, O2- generated by xanthine-xanthine oxidase, and 8 times 10(-4) M hydrocortisone inhibited the C3b receptor, but did not inhibit the Fc receptor. In neutrophils, the selective effect of the various inhibitors suggests that the Fc and C3b receptors are distinct entities