Effects of alpha-2 adrenoreceptor blockade by yohimbine on the hormonal response to hypoglycaemic stress in normal man

In order to evaluate the effect of alpha-2 adrenoreceptor blockade on the ACTH response to insulin-induced hypoglycaemia, six normal men were studied with and without yohimbine (30 mg p.o.) premedication. Despite a similar hypoglycaemic stimulus and significant suppression of the growth hormone response (P less than 0.05), no change was observed in basal or stimulated plasma ACTH, cortisol, arginine vasopressin (AVP) or prolactin responses following yohimbine. We conclude that alpha-2 adrenoceptor blockade with yohimbine does not significantly affect the ACTH response to hypoglycaemia in man.     

Functional bioassays utilizing zooplankton: a comparison

Functional zooplankton bioassays based on ingestion, reproduction and respiration are described, with methods for a new ingestion bioassay included. All bioassays are compared using three indices, including the variability of controls, the range of experimental responses, and a listing of contaminants causing inhibition/stimulation of response. The ingestion bioassay showed the greatest range of response, and was sensitive to pesticides, PCBs and heavy metals. It was also commonly characterized by a hormesis response. The reproduction bioassay showed the lowest variability, illustrated a reduced range of response, and was sensitive to nutrients and heavy metals. In one study, the respiration bioassay was sensitive only to PCBs.     

Quantitative genetics of seed size variation inPhlox

Summary Because seed size is often associated with survival and reproduction in plant populations, genetic variation for seed size may be reduced or eliminated by natural selection. To test this hypothesis we assessed genetic sources of variation in seed size in a population ofPhlox drummondii to determine whether genetic differences among seeds influence the size they attain. A diallel cross among 12 plants from a population at Bastrop, Texas, USA allowed us to partition variance in the mass of seeds among several genetic and parental effects. We found no evidence of additive genetic variance or dominance genetic variance for seed mass in the contribution of plants to their offspring. Extranuclear maternal effects accounted for 56% of the variance in seed mass. A small interaction was observed between seed genotype and maternal plant. Results of this study support theory that predicts little genetic variation for traits associated with fitness.     

The occurrence and distribution of certain polypeptides within the human carotid body

Summary Both carotid bodies from 26 patients coming to necropsy were fixed in 10% neutral buffered formalin and sections 4 m thick were stained for various peptides by use of the immunogold technique. The results show that the human carotid body contains met- and leu-enkephalin, substance P, vasoactive intestinal peptide (VIP), neurotensin and bombesin. The distribution of these six peptides within the carotid body differs. Thus met- and leu-enkephalin are both present predominantly within glomic chief cells but with a marked tendency to favour the dark variant of these cells. Substance P and VIP both show a weak immunoreactivity in comparison to the enkephalins and are present in all three variants of chief cell. Neurotensin shows the weakest immunoreactivity of all and is restricted to a few glomic chief cells in a minority of cases. Bombesin also shows a weak immunoreactivity in glomic chief cells but a strong reaction in glomic arteries and arterioles. In these vessels bombesin appears to be confined to smooth muscle cells in the media but we cannot say whether it is secreted by them or merely bound to receptor sites on their membranes. These findings are related to quantitative data on the concentration of peptides in the human carotid body from a previous paper with which we were associated.     

Ultrastructure of pericytes in early stages of histamine-induced inflammation

Physiological and ultrastructural assessment of changes in the walls of venules in the rat cremaster muscle after administration of histamine indicates that pericytes have essential roles in the normal functioning of venules during inflammation. Fluorescein-labelled albumin was used to quantitate macromolecular leakage and to select suitable venules for ultrastructural analysis 4 and 7 minutes after addition of histamine. Pericytes were concentrated over endothelial cell junctions and gaps. At 4 minutes, when albumin leakage was becoming detectable, gaps between endothelial cells were observed in the venule wall. In 24 serially sectioned gaps, pericytes formed covers, with contact points to the endothelial cells along the sides of the gaps. At 7 minutes, when albumin leakage was maximal, gaps with pericyte covers were still evident, but more commonly observed were pericyte covers over closed endothelial cell junctions. Spaces between the innermost pericytes and endothelial cells were enlarged by an order of magnitude, from 95 nm in controls to 872 nm at 4 minutes and 958 nm at 7 minutes. Pericytes formed coverings or bridges over inclusions of extravasated cells, fluid, proteins, and the vascular label monastral blue. The data indicate that pericytes protect the endothelial lining of venules during histamine-induced inflammation by forming a cohesive covering across gaps.     

Light-evoked walking in crayfish: Behavioral and neuronal responses triggered by the caudal photoreceptor

The caudal photoreceptors (CPRs) of crayfish (Procambarus clarkii) can trigger walking and abdominal movements by their response to light.

Post-receptor modulation of the effects of cyclic AMP in isolated cardiac myocytes

Summary The actions of cyclic AMP are subject to several levels of post-receptor modulation in cardiac tissue. Isoproterenol and prostaglandin E₁ both stimulate cAMP accumulation, but only isoproterenol causes activation of particulate cAMP-dependent protein kinase, leading to activation of phosphorylase kinase and glycogen phosphorylase, and inhibition of glycogen synthase. Through the use of isolated, adult ventricular myocytes, we have determined that the hormone-specific activation of glycogen phosphorylase is due to subcellular compartmentation of cAMP. There is some evidence that cyclic nucleotide phosphodiesterases, whose activity is stimulated by alpha₁-adrenergic agonists in isolated myocytes, may have a role in compartmentation. Phosphoinositide hydrolysis is stimulated by alpha, and muscarinic agonists, presumably leading to activation of protein kinase C, which in turn has multiple effects on hormone-sensitive adenylate cyclase.Abbreviations cAMP Adenosine-3,5-Cyclic Monophosphate - cGMP Guanosine-3,5-Cyclic Monophosphate - G_i, G_S Guanine nucleotide-binding proteins linked to inhibition and stimulation, respectively, of adenylate cyclase - GTP Guanosine-5-triphosphate - PDE Cyclic Nucleotide Phosphodiesterase - PGE₁ Prostaglandin E₁     

A third class I major histocompatibility complex antigen encoded by a gene in the D region of the H-2 d haplotype recognized by cytotoxic T lymphocytes

The D region of the H-2 ^d haplotype contains five class I genes: H-2D ^d , D2 ^d , D3 ^d , D4 ^d and H-2L ^d . Although previous studies have suggested the presence of D-end encoded class I molecules in addition to H-2D^d and H-2L^d, segregation of genes encoding such molecules has not been demonstrated. In this report we have used cãtotoxic T lymphocytes (CTL) to examine the D region of the H-2 ^d haplotype for the presence of additional class I molecules. CTL generated in (C3H × B6.K1)F₁ (K ^k D ^k , K ^b D ^b ) mice against the hybrid class I gene product Q10^d/L^d expressed on L cells cross-react with H-2L^d but not H-2D^d molecules, as determined by lysis of transfected cells expressing H-2L^d but not H-2D^d. Although H-2L^d-specific monoclonal antibodies (mAb) completely inhibit H-2L^d-specific CTL from killing B10.A(3R) (K ^b D ^d L ^d ) target cells, only partial inhibition of anti-Q10 CTL-mediated lysis was observed, suggesting the presence of an additional D-end molecule as a target for these latter CTL. To identify the region containing the gene encoding the Q10 cross-reactive molecule, we show that anti-Q10 CTL lyse target cells from a D-region recombinant strain B10.RQDB, which has H-2D ^d , D2 ^d , D3 ^d , D4 ^d , and H-2D ^b but not the H-2L ^d H-2 ^d , and H-2L ^d (including D2 ^d , D3 ^d , and D4 ^d , lacks this anti-Q10 CTL target molecule. Together, these data demonstrate that a class I gene mapping between H-2D ^d and H-2L ^d encodes an antigen recognozed by anti-Q10 CTL. A likely candidate for this gene is D2 ^d , D3 ^d or D4 ^d .