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S M Laird

Publications and source records attributed to S M Laird.

At least 55 records · Page 3Linked to original sources
PubMed1991

The biosynthesis of aldosterone.

The cellular mechanisms for aldosterone biosynthesis are incompletely understood. Although the enzymes involved are now well characterized, the dynamics of aldosterone secretion in a variety of rat adrenal preparations are not consistent with the concept that freshly synthesized corticosterone is an important intermediate. In whole glomerulosa tissue preparations, aldosterone is more readily formed from endogenous precursors than from an added radioactive precursor, such as [3H]pregnenolone, and in the in situ perfused gland preparation, aldosterone responses to stimulation, for example by ACTH, are significantly more rapid than those of corticosterone, suggesting a tissue source of steroid substrate for aldosterone production other than corticosterone. The only steroid which is stored in rat adrenal glomerulosa tissue to any extent is 18-hydroxydeoxycorticosterone (18-OH-DOC), and this pool has been located in plasma membrane fractions. It is lost on preparation of collagenase dispersed glomerulosa cells. Since dispersed glomerulosa cell preparations produce significantly less aldosterone, relative to corticosterone, than incubated intact whole glomerulosa, it is plausible that this tissue pool (which is not found in the inner zones) is the immediate precursor for aldosterone formation. Further evidence shows that trypsin, which stimulates aldosterone (and 18-hydroxycorticosterone) production in rat intact glomerulosa tissue, but not in dispersed cells, stimulates translocation of protein kinase C to the plasma membrane. It is plausible that one function of protein kinase C in the rat adrenal zona glomerulosa is to mobilize membrane sequestered 18-OH-DOC for conversion to aldosterone.

Aldosterone↗
PubMed1991

Control of steroidogenesis by the calcium messenger system in human adrenocortical cells.

The involvement of the calcium messenger system in the control of steroidogenesis in the rat and bovine adrenal cortex has been studied extensively. However the role of these second messengers in the control of human adrenocortical function is not established. This was therefore studied by incubating collagenase-dispersed human adrenocortical cells with the calcium ionophore A23187 and the protein kinase C activator phorbol 12-myristate 13-acetate (TPA). The effects of the calcium channel blocker verapamil on basal and stimulated steroidogenesis were also studied. Both TPA (1 pmol/l-10 mumol/l) and A23187 (1 nmol/l-10 mumol/l) caused a dose-dependent increase in cortisol, aldosterone and corticosterone production. Verapamil (10 mumol/l) inhibited the increase in aldosterone, corticosterone and cortisol produced in response to ACTH(1-24), potassium, and desacetyl-alpha MSH. Unlike previous results in the rat, these effects were not specific for aldosterone secretion. The results suggest that, as in other species, calcium mobilization and protein kinase C activation have a role in the control of steroidogenesis in the human adrenal cortex. However, in contrast to the rat, these mechanisms appear to be involved in the control of steroidogenesis in both the zona glomerulosa and inner zone cells.

Adrenal Cortex↗
PubMed1990

Trypsin stimulation of aldosterone and 18-hydroxycorticosterone production by rat adrenal zona glomerulosa tissue is mediated by activation of protein kinase C.

When rat adrenal whole capsules, containing the zona glomerulosa, were incubated, addition of the protein kinase C inhibitors TMB-8 (10 mumol/l), W7, H7, polymyxin-B and sphingosine (all 1 mumol/l) was found to inhibit the steroidogenic response to trypsin. Aldosterone and 18-hydroxycorticosterone were strongly, and corticosterone moderately, affected, while the production of 18-hydroxydeoxy-corticosterone was neither stimulated by trypsin nor inhibited by the protein kinase C inhibitors. Addition of neomycin, which prevents substrate interaction with phospholipase C, also inhibited the response to trypsin, while addition of phospholipase C itself stimulated aldosterone, 18-hydroxycorticosterone and corticosterone production with the same tissue sensitivity as trypsin. Addition of phospholipase A2 had no effect. Direct assay of protein kinase C activity showed that trypsin stimulation effected the translocation of Ca2+/phospholipid-activated protein kinase C from the cytosolic to the membrane fraction. When glomerulosa tissue was incubated with [32P]ATP, and cytosolic proteins were subjected to isoelectric focusing on polyacrylamide gels, autoradiography showed that incorporation of 32P into several protein components was increased by trypsin stimulation. It was concluded that trypsin exerts its stimulatory effects on steroidogenesis by activating protein kinase C; not, however, by generating the Ca2+/phospholipid-independent fragment, but possibly by enhancing the activity of phospholipase C.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1989

Specific effects of agonists of the calcium messenger system on secretion of 'late-pathway' steroid products by intact tissue and dispersed cells of the rat adrenal zona glomerulosa.

Recent data have implicated the phosphatidylinositol/calcium second-messenger system in the control of aldosterone secretion by the adrenal zona glomerulosa. However, in the rat adrenal there are few reports of a direct effect of protein kinase C activation on steroid secretion, while the effects of calcium mobilization may be variable. Since the rat adrenal zona glomerulosa is sensitive to the mode of tissue preparation, these mechanisms were reinvestigated in intact (non-dispersed) capsular tissue and collagenase-dispersed zona glomerulosa cells. Steroidogenesis in the intact zona glomerulosa was markedly affected by agonists of the calcium messenger system. Most notably, aldosterone and 18-hydroxycorticosterone (18-OH-B) secretion were stimulated by A23187 (100 nmol to 10 mumols/l) and BAY K 8644 (500 nmol/l). Phorbol 12-myristate 13-acetate (TPA; 1 pmol to 1 mumol/l) stimulated aldosterone secretion at all doses and caused a dose-dependent increase in 18-OH-B and 18-hydroxydeoxycorticosterone (18-OH-DOC) secretion. Corticosterone secretion was slightly increased in the presence of A23187 but not by TPA or BAY K 8644. Production of 18-OH-DOC was unaffected by A23187 and BAY K 8644. The calcium channel antagonist verapamil (10 mumols/l) inhibited ACTH-stimulated aldosterone secretion by the intact zona glomerulosa but had no effect on corticosterone secretion. Verapamil (10 mumols/l) also inhibited the increase in aldosterone secretion by collagenase-dispersed zona glomerulosa cells stimulated by ACTH (100 fmol to 100 nmol/l), angiotensin II (100 pmol to 10 nmol/l) and potassium (5.9 and 8.4 mmol/l); stimulated corticosterone secretion was unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

18-Hydroxycorticosterone↗
PubMed1989

Actions of desacetyl-alpha-melanocyte-stimulating hormone on human adrenocortical cells.

The responses of human adrenocortical cells to stimulation by ACTH(1-24), desacetyl-alpha-MSH, alpha-MSH and angiotensin II amide have been compared. Both desacetyl-alpha-MSH, thought to be the major form of the peptide in the human pituitary and in circulating plasma, and alpha-MSH caused a significant stimulation of aldosterone, corticosterone and cortisol secretion. Significant stimulation of the production of these steroids was obtained with desacetyl-alpha-MSH at a concentration of 1 nmol/l, while the response to alpha-MSH was considerably less sensitive, with a minimum effective concentration of 0.1 mumol/l. These values compared with minimum effective concentrations of 1 pmol/l for ACTH and 0.1 mumol/l for angiotensin II amide. Although cell types were not separated, it is possible to conclude that none of the peptides showed any specificity for the zona glomerulosa, and in each case the same minimum effective concentration of peptide was required for both aldosterone and cortisol secretion. Yields of steroid obtained under conditions of maximal stimulation by ACTH(1-24), alpha-MSH and desacetyl-alpha-MSH were at least three to five times the basal output of aldosterone, four to eight times that for corticosterone and more than seven to sixteen times that for cortisol. Angiotensin II amide was a relatively poor stimulant with maximal stimulation only 1.5 x basal. In these experiments the minimum effective concentration for desacetyl-alpha-MSH (1 nmol/l) was close to the circulating concentration of desacetyl-alpha-MSH (0.3 nmol/l) in man, and it is thus possible that this peptide may have a physiological role in the control of adrenocortical function.

Adrenal Cortex↗
PubMed1988

Monoclonal antibodies against rat adrenocortical cell antigens.

Cell lines secreting antibodies directed against rat adrenocortical cell antigens have been produced using hybridoma techniques. As tested by immunofluorescent staining, eleven of these antibodies were specific for rat adrenocortical cells in that they did not interact with rat adrenal medulla, liver, muscle, ovary or kidney cells. Two of these antibodies were studied in greater detail. One interacted with an antigen present only in adrenal fasciculata and reticularis cells (inner zone antibody, IZA). The expression of the antigen with which this antibody interacted was increased by in vivo treatment with ACTH. The other antibody interacted with an antigen present in all three adrenocortical cell types (adrenocortical antibody ACA). Expression of this antigen was unaffected by ACTH treatment. The effect of both antibodies on steroid biosynthesis by mitochondrial and microsomal preparations of zona glomerulosa and inner zone tissue was tested. For these experiments, the antibodies were purified from culture media by Protein-A-Sepharose affinity chromatography. ACA had no effect on steroidogenesis by any preparation. IZA specifically decreased the production of 18-hydroxydeoxycorticosterone from deoxycorticosterone by the inner zone microsomal and mitochondrial fraction. The results suggest that the IZA antigen is found predominantly in the rat adrenal inner zone and that the antibody may be useful in monitoring adrenocortical zonation. In addition, the antigen would appear to have a functional role in steroid metabolism.

Adrenal Cortex↗
PubMed1988

Steroid sequestration within the rat adrenal zona glomerulosa.

Accumulated data from in-vitro experiments have suggested that 18-hydroxysteroids may be stored within the intact rat adrenal zona glomerulosa. The phenomenon was further investigated by comparing the amount of steroid remaining in the zona glomerulosa tissue with that secreted into the media during incubation in vitro. The results showed that 18-hydroxydeoxycorticosterone (18-OH-DOC) and 18-hydroxycorticosterone (18-OH-B) were retained within the tissue against a considerable concentration gradient, with smaller amounts of aldosterone and corticosterone. Lysis of the intact zona glomerulosa, by preincubation in distilled water, yielded an enriched plasma membrane preparation. After subsequent incubation in Krebs-Ringer bicarbonate this preparation contained significantly more 18-OH-DOC than did the intact tissue, suggesting that tissue-sequestered 18-OH-DOC is normally metabolized to other products. These may include 18-OH-B and aldosterone. Fractionation of homogenized intact zona glomerulosa and the enriched plasma membrane preparation by density gradient centrifugation showed that tissue 18-OH-DOC banded in fractions of density 1.063-1.21 g/ml and that its distribution was highly correlated with protein. Corticosterone, 18-OH-B and aldosterone banded like added free [3H]18-OH-DOC in fractions of density less than 1.006 g/ml. The results suggest that 18-OH-DOC is the major sequestered steroid within the rat adrenal zona glomerulosa and that this sequestration is attributable to the association of 18-OH-DOC with a high-density component of the plasma membrane.

18-Hydroxycorticosterone↗
PubMed1987

Control of aldosterone secretion in zona glomerulosa cell suspensions and in the perfused adrenal gland of the rat.

The secretion of aldosterone and its responses to stimulation have been studied in rat adrenal zona glomerulosa tissue incubated as intact capsules or as collagenase-dispersed cell suspensions, and in intact perfused rat adrenal glands. Several differences are apparent in the functions of the various preparations. Aldosterone secretion rates are similar in incubated intact capsules and in the perfused gland. Relative to corticosterone, lower yields of aldosterone are obtained in dispersed glomerulosa cell in vitro. This may be related to the loss in the dispersed cells of a pool of tissue steroid (aldosterone or a precursor) which is revealed only in intact tissue incubations by trypsin stimulation of aldosterone secretion. Trypsin-released aldosterone is increased by prior dietary sodium restriction. In addition, differences occur in the responses of dispersed cells and perfused glands to stimulation. Perfused glands from animals on a normal diet are less sensitive to stimulation by ACTH or alpha-MSH, but more sensitive than dispersed cells to angiotensin II amide. In the perfused gland, sensitivity of response (lowest effective concentration) to all three stimulants is increased by prior dietary sodium restriction, in contrast to dispersed cells in which increased sensitivity has been reported only to alpha-MSH. The perfused gland is particularly sensitive to angiotensin II amide, and a bolus administration of 1 amol gives significant stimulation in glands from animals on low sodium intake. Electrical (field) stimulation or dopamine administration at 10(-6) mol/l (which is ineffective in dispersed cells) both depress aldosterone secretion by the perfused gland. The data suggest that the sequestered pool of steroid is utilized in the perfused gland for aldosterone secretion. They furthermore suggest that in the intact gland there are mechanisms, which involve neural components, for intraglandular regulation of aldosterone secretion, which are lost in dispersed cells in vitro. Such mechanisms may be involved in sensitivity increases in sodium depletion.

Adrenal Glands↗
PubMed1986

The actions of N-terminal fragments of corticotrophin on steroidogenesis in dispersed rat adrenal cells in vitro.

The finding that the rat adrenal zona glomerulosa cell shows specific sensitivity to stimulation by alpha-MSH and related peptides has been confirmed both in vivo and in vitro, raising the possibility that alpha-MSH may have a physiological role in the control of glomerulosa function and aldosterone secretion. To define more closely the structural features which confer teh specificity of the glomerulosa response, other ACTH derived peptides have been tested for their specificity of actions on rat adrenal cells in vitro. The peptides tested were ACTH(5-24), ACTH(1-12), ACTH(1-14), ACTH(1-15), ACTH(1-16) and ACTH(1-17). Their actions were compared with those of alpha-MSH and ACTH(1-24). All of the ACTH-derived peptides stimulated glomerulosa corticosterone production with sensitivities similar to that of alpha-MSH; minimum effective concentration was 10 nmol/l. Also, like alpha-MSH, the shorter ACTH peptides stimulated aldosterone production only relatively weakly in these cells from animals on normal sodium intake. Only ACTH(5-24), ACTH(1-16) and ACTH(1-17) stimulated fasciculata/reticularis cells at concentrations up to 1 mumol/1. The actions of all of the shorter peptides were thus unlike those of ACTH(1-24) which stimulates both cell types with approximately equal sensitivity, and which furthermore strongly stimulates aldosterone production. The data suggest that the 18-24 region of the ACTH molecule contains the signal for a fasciculata/reticularis response, and the region 1-13 that for glomerulosa specificity. They confirm the view that, in the rat, alpha-MSH itself may be the specific pituitary glomerulosa-stimulating agent which much experimental work has predicted. They also indicate that synthetic ACTH(1-17) analogues should be used with caution.

Adrenal Cortex↗
PubMed1975

Treatment of trichomoniasis in the female. A comparison of metronidazole and nimorazole.

The effectiveness of metronidazole (Flagyl) and nimorazole (Naxogin) has been compared by using these drugs in the recommended dosage in alternate patients in a series of 218 consecutive cases of vaginal trichomoniasis. Follow-up tests in 100 patients treated with metronidazole and 97 treated with nimorazole indicated cure-rates of 95 and 82 per cent. respectively. Male consorts were examined and given treatment on epidemiological grounds in about 70 per cent. of both treatment groups. Both drugs were free from significant side-effects. The causes of treatment failure in trichomoniasis are discussed and the desirability of relating dosage to the patient's body-weight is suggested. This factor may be especially important in deciding the dosage given on epidemiological grounds to the male consorts. It may also be an important advantage in the current trend of treating trichomoniasis in both sexes with larger doses over a much shorter time.

Administration, Oral↗