Adrenocortical responses to adrenocorticotrophin in the rat

The time course of plasma adrenocorticotrophin (ACTH), adrenal cyclic AMP, adrenal corticosterone, and plasma corticosterone was measured in male Sprague-Dawley rats whose endogenous release of ACTH had been blocked (1) following rapid injections of 100 and 300 ng ACTH/100 g body weight, i.v., (2) during prolonged infusions at rates of 1, 2, and 4 ng ACTH/min per 100 g body weight, and (3) after termination of 30-min infusions at rates extending from 0.06 to 8 ng ACTH/min per 100 g body weight. Following injections, the time course of the variables is similar to the one simulated from our models of adrenal cortical secretion, including the simulation of an intermediate variable of our models of the adrenal cortex cell which was presumed to correspond to cyclic AMP. However, during prolonged infusions there is an unexpected overshoot of adrenal cyclic AMP content whereas adrenal and plasma corticosterone concentrations rise to a steady-state value without overshoot. The total amount of cyclic AMP gradually increases following the three increasing infusion rates of ACTH whereas similar levels of plasma corticosterone concentrations are reached at steady state; therefore the saturation of the adrenal cortical secretion is due to a step ulterior to cyclic AMP formation in the steroidogenesis. After 30-min infusions, plasma corticosterone concentration reaches its maximal value following a rate of ACTH input which evokes only a 4-fold increase in adrenal cyclic AMP content; however, there is a 250-fold increase of adrenal cyclic AMP with respect to control value following the higher rates of infusion of ACTH.

Mapping of a new hem gene in Escherichia coli K12

A new type of haem-deficient mutant was isolated in Escherichia coli K12 by neomycin selection. The mutant, designated SASX38, accumulated uroporphyrin, coproporphyrin and protoporphyrin. Since it possessed normal ferrochelatase activity, it was assumed to be deficient in protoporphyrinogen oxidase activity. The gene affected in the mutant was designated hemG. Mapping of the hemG gene by phage P1-mediated transduction showed that it was located very close to the chlB gene (frequency of cotransduction 78.7%), between the metE and rha markers. This location is distinct from the other known hem loci in E. coli K12.

Melatonin-and serotonin-stimulated release of vasopressin from rat neurohypophysis in vitro

In order to study the control of vasopressin-release, the effect of a series of potential agents was studied in an in vitro perifusion system of rat neurohypophysis after in vivo treatment with nialamide, a monoamine oxidase inhibitor. In this system, metlatonin stimulated vasopressin-release in a dose-dependent manner (1 x 10-8 to 1 x 10-3 M). Serotonin (1 x 10-3 M) also led to a significant increase of vasopressin-release whereas quipazine (1 x 10-3 M), a putative serotonin agonist and monoamine oxidase inhibitor, caused a 3-fold stimulation of the release of the neurohormone. The stimulatory effects of melatonin and serotonin were prevented by omission of Ca2+ combined to an excess of Mg2+ (12mM) in the perifusion medium. 1 x 10-6 M somatostatin did not affect basal or melatonin-stimulated vasopressin-release. These results show that melatonin and serotonin can have a direct stimulatory effect on vasopressin release at the neurohypophyseal level.

Effect of gonadal steroids on the luteinizing hormone and follicle-stimulating hormone response to 8-bromo-adenosine 3',5'-monophosphate in anterior pituitary cells in culture

-8-Bromo-cAMP stimulated the release of LH (approximately 20-fold) and FSH (approximately 2-fold) in control rat anterior pituitary cells in primary culture. 8-Bromo-cAMP-induced LH release was 2-3 times greater in cells preincubated for 48 h in the presence of 10(-8) M 17 beta-estradiol (E2). The LH response to 10(-10) M LHRH was similarly increased by E2 pretreatment whereas progesterone (P), which had no effect on the response to 8-bromo-cAMP, led to a reduction of the stimulatory effect of E2 on the LH response to the neurohormone. Preincubation with 10(-8) M testosterone (T) decreased the LH response to 8-bromo-cAMP by about 40%, whereas the response to LHRH was 80% inhibited. 8-Bromo-cAMP-induced FSH release was slightly increased in cells preincubated with E2 but was greatly augmented in cells treated with E2 + P. Basal FSH release was slightly increased (40%) after preincubation with P or T whereas the response to 8-bromo-cAMP was not significantly affected. The sensitivity of the FSH response to LHRH was increased by E2 whereas P and T led to a stimulation of the maximal FSH response to LHRH with no significant effect on the LHRH ED50 value. The present data indicate that P and E2 exert their effects on LH and FSH release at steps before and after cAMP formation, respectively. T appears to act at both steps on the release of the two gonadotropins.

Stimulation of glucagon release by addition of anti-stomatostatin serum to islets of Langerhans in vitro

Addition of anti-somatostatin serum to rat islets of Langerhans which had been previously maintained in organ culture for 48h, resulted in a marked stimulation of glucagon release with no change in the rate of insulin secretion during the entire 90 min period during which the secretion of both hormones was followed. Prior saturation of the anti-somatostatin serum with somatostatin prevented the stimulatory acting on glucagon release. These data strongly suggest a physiological role for endogenous somatostatin in the control of glucagon secretion.

Isolation and partial characterization of an Escherichia coli mutant resistant to colicin A

An Escherichia coli K12 mutant resistant to colicin A-CA31 apparently through loss of its receptor sites has been isolated and partially characterized. Resistance to colicin A was accompanied with a decreased sensitivity to colicins L-398 and E2-CA42, and to acridine dyes. The mutant strain displayed the same general pattern of tolerance or sensitivity as the parent strain towards eight antibiotics, colicins C, D, E1, E3, F2, F3, G, I, K, and N; phages T1, T2, T5, T6, T7, F2, lambda vir, P1kc, phi 80, and BF23; and to methylene blue, triphenyltetrazolium chloride, ethylenediaminetetraacetate (EDTA), deoxycholate, and sodium dodecyl sulfate. Conjugation and transduction experiments showed that a locus controlling resistance to colicin A-CA31 mapped at 21 min on the genetic map of this E. coli K12 strain.

Decreased activity of colicins K-K235, A-CA31, C-CA57, and E2-CA42 upon sensitive Escherichia coli strains in the presence of cyclic 3′,5′–adenosine monophosphate

The addition of cyclic 3′,5′-adenosine monophosphate (c-AMP) at a final concentration of 3 mM to nutrient broth significantly decreased the lethal activity of crude preparations of colicins A-CA31, K-K235, E2-CA42, and C-CA57 upon three different sensitive Escherichia coli strains. A protective effect of c-AMP on cell viability could also be shown in mixed cultures of the colicinogenic and the sensitive strains. Furthermore, the addition of c-AMP significantly reversed, in the sensitive E. coli ROW strain, the inhibition of triphenyltetrazolium chloride (TTC) reduction caused by the bacteriocins. However, the activities of colicin E3-CA38 on cell viability and reduction of TTC were not overcome markedly by exogenously added c-AMP. None of seven other cyclic nucleotides tested appeared to duplicate the protective effect of c-AMP against colicin A-CA31. The results indicate that for colicins K-K235, A-CA31, C-CA57, and E2-CA42 but not for colicin E3-CA38, there may be similar steps in the translocation of effects to sensitive targets and (or) a closely related mode of action reversible by c-AMP.

Inhibition of colicin production by fermentable sugars

Several fermentable sugars (glucose, lactose, arabinose, and to a lesser extent sucrose) were found to reduce colicin production in a strain of Shigella sonnei P9 (colicins E2 and I) and in a strain of Escherichia coli CA31 (colicin A). Inositol and adonitol, which are apparently not fermented by these colicinogenic strains, did not seem to affect colicin production under our experimental conditions. The results indicated that the production of colicins E2 and A, like the formation of certain R-factor-coded enzymes, may be subject to catabolite repression. A system of mixed cultivation in nutrient broth, of colicinogenic and sensitive strains, was also used; under these conditions, the number of viable units of the sensitive indicator strain decreased more rapidly in the absence than in the presence of added glucose.