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B T Pickering

Publications and source records attributed to B T Pickering.

At least 37 records · Page 2Linked to original sources
PubMed1984

Variations in oxytocin, vasopressin and neurophysin concentrations in the bovine ovary during the oestrous cycle and pregnancy.

Bovine ovaries were obtained from the abattoir and corpora lutea were classified as: (1) early luteal phase (approximately Days 1-4); (2) mid-luteal phase (Days 5-10); (3) late luteal phase (Days 11-17); (4) regressing (Days 18-20) and (5) pregnant (Days 90-230). In addition, preovulatory follicles and whole ovaries without luteal tissue were collected. Concentrations of oxytocin, vasopressin, bovine neurophysin I and progesterone were measured in each corpus luteum by radioimmunoassay. Progesterone and neurophysin I levels increased from Stage 1 to Stage 2, plateaued during Stage 3 and declined by Stage 4. Oxytocin and vasopressin concentrations increased from Stage 1 to Stage 2 but declined during Stage 3 and were low (oxytocin) or undetectable (vasopressin) in follicles, whole ovaries and pregnancy corpora lutea. Therefore the concentrations of both peptide hormones were maximal during the first half of the cycle and declined before those of progesterone. The high concentration of oxytocin within the corpus luteum coupled with the presence of bovine neurophysin I suggests that oxytocin is synthesized locally.

Animals↗
PubMed1984

Presence of a neurophysin-like precursor in the green turtle (Chelonia mydas).

A glycoprotein of neurohypophysial origin was found to have cofractionated with FSH prepared from pituitary glands of the green turtle, Chelonia mydas. Antiserum raised against this preparation contained high antibody titres and affinity for the neurohypophysial component and allowed development of a specific radioimmunoassay to monitor its purification and distribution in the brain. Immunocytochemistry revealed that the glycoprotein was concentrated in the pars nervosa and associated nerve tracts passing through the median eminence to the supraoptic and paraventricular nuclei; similar distributions were observed in turtles and rats. The antiserum to the turtle material bound radiolabelled rat vasopressin (VP)-neurophysin and precipitated precursors of this neurophysin, but it did not cross-react with rat oxytocin-neurophysin. An amino-terminal alanine was also consistent with the structure of rat VP-neurophysin, but the turtle molecule was larger than the corresponding rat molecule. Limited tryptic digests of the turtle glycoprotein contained two components, one of which bound to lysine VP. Both components contained carbohydrate, but only the one which bound to VP cross-reacted in a radioimmunoassay for rat VP-neurophysin. The apparent surge in plasma immuno-FSH at the time of oviposition previously described in the turtle probably represented release of a neurophysin-like 'carrier' molecule associated with secretion of the neurohypophysial hormone (e.g. arginine vasotocin; AVT) responsible for oviduct contractility. These data suggest that the neurohypophysial glycoprotein represents a partially processed AVT precursor and provide the first biochemical evidence of a mammalian-like biosynthetic pathway for neurohypophysial hormones in a non-mammalian species.

Amino Acids↗
PubMed1983

Analysis of the neurohypophyseal components accumulating in the supraoptic nucleus of the rat after injection of colchicine.

[35S]Cysteine has been injected into the supraoptic nuclei of normal rats and of animals given 7 micrograms colchicine into the cerebrospinal fluid to inhibit transport of neurosecretory granules. Analysis of extracts of the supraoptic nuclei 20 min or 6 h after isotope injections showed that (i) colchicine does not affect biosynthesis, i.e., incorporation of tracer into the common precursors of neurohypophyseal hormones and their associated neurophysins, and (ii) processing of precursors inside the arrested granules proceeds normally.

Animals↗
PubMed1983

Characterization of oxytocin, vasopressin, and neurophysin from the bovine corpus luteum.

Acid extracts of corpora lutea collected from nonpregnant cows were found to contain oxytocin, arginine vasopressin, and neurophysin. The inhibition curves of the oxytocin and vasopressin extracts showed parallelism with the appropriate standard preparations in specific RIAs and eluted at the same position as the standards using high performance liquid chromatography (HPLC). The neurophysin extract showed parallelism in a bovine neurophysin I RIA and had a similar elution position to the standard on both Sephadex G-50 and HPLC. However, its immunoreactive profile on HPLC differed slightly from that obtained with hypophyseal bovine neurophysin I. In nonpregnant cows the oxytocin content (about 1 microgram g-1 wet wt of tissue) was three orders of magnitude greater than the vasopressin content. Levels of luteal oxytocin were considerably lower in pregnant animals. These results show that the bovine ovary is a rich source of neurohypophysial peptides and suggest that oxytocin biosynthesis may occur within the corpus luteum.

Animals↗
PubMed1982

Precursors in the biosynthesis of vasopressin and oxytocin in the rat. Characteristics of all the components in high-performance liquid chromatography.

A reverse-phase high performance liquid-chromatography (h.p.l.c.) protocol has been developed, whereby all the major known posterior-pituitary components that are derived from the processing of pro-oxytocin and pro-vasopressin can be separated one from another. Thus, in a single chromatographic step, it has been possible to separate vasopressin (VP), oxytocin (OT), oxytocin-neurophysin (rOT-Np), vasopressin-neurophysin (rVP-Np) and vasopressin-glycopeptide (rVP-GP) from acid extracts of the neurointermediate lobes of rat pituitary glands. All these peptides except rVP-GP were labelled in the neural lobe by 24h after a hypothalamic injection of [35S]cysteine, whereas all except VP were labelled by 24h after a similar injection of [3H]leucine. Three major labelled proteins were isolated from 20 min [35S]cysteine-injected rats when extracts of the supraoptic nucleus were subjected to Sephadex G-75 chromatography, h.p.l.c. and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Immunoprecipitation with antisera raised against rat neurophysins, VP and OT revealed 21000- and 19000-mol.wt. common precursors to VP and rVP-Np and a 15000-mol.wt. common precursor to OT and rOT-Np. Some immunoreactive rVP-Np could occasionally be detected in the Vo of Sephadex G-75 chromatograms of Wistar rat supraoptic-nucleus extracts, but no evidence of [35S]neurophysin in this fraction was obtained from h.p.l.c. fingerprinting of its S-carboxymethylated tryptic digests. Radioimmunoassay for rVP-Np and rOT-Np revealed that about 70-80% of the total recovered immunoreactive neurophysin (IR-Np) in the supraoptic nucleus eluted from Sephadex G-75 and h.p.l.c. in the positions of rVP-Np and rOT-Np. Evidence is presented for an approx. 20000-mol.wt. rOT-Np in both Wistar and Brattleboro rats and for an approx. 20000-mol.wt. component in the Brattleboro rat that is recognized by vasopressin-neurophysin antisera.

Animals↗
PubMed1981

Effects of small doses of colchicine on the components of the hypothalamo-neurohypophysial system of the rat.

Small doses (3.5 micrograms and 7 micrograms) of colchicine injected intracisternally caused an interruption of transport of secretory material from the supraoptic and paraventricular nuclei of the hypothalamus to the neural lobe of the pituitary gland. Transport was assessed by direct measurement of the incorporation of [35S] cysteine into neurophysins, by radioimmunoassay of accumulated material in discrete areas of the system and by immunocytochemistry. The larger dose (7 micrograms) switched off transport completely during the first 24h but the system began to recover within three to four days. Colchicine had little, if any, effect on synthesis; comparison of the relationships of the apparent amounts of immunoreactive neurophysins and immunoreactive hormones in the arrested product led to the conclusion that processing of the hormone precursors continues within secretory granules which accumulated in the perikarya.

Animals↗
PubMed1981

Effects of tunicamycin on the hypothalamo-neurohypophysial system of the rat.

Intracisternal injections of tunicamycin, an inhibitor of glycosylation, decreased the incorporation of [35S]cysteine into the neurophysins in the rat neurohypophysis. Histochemical and immunocytochemical studies showed that there was no concomitant decrease in the amount of secretory product in the perikarya of the hypothalamo-neurohypophysial neurones. Indeed there was an increase, although this was not associated with neurosecretory granules as judged electron-microscopically. Tunicamycin led to the formation of so-called "colloid droplets" which were immunopositive and of which the ultrastructural correlates appeared to be product-filled dilatations of the rough endoplasmic reticulum. The observations are interpreted to suggest that glycosylation plays a rôle in the packaging of secretory material in the hypothalamo-neurohypophysial system.

Animals↗
PubMed1981

Fate of neurohypophysial granule membranes after secretion in the rat: generation of a new apparent organelle by freezing and thawing secretory granules.

The contents and membranes of the secretory granules in the rat neurohypophysis were labelled in vivo with [35S]cysteine and [3H]choline respectively. Density-gradient centrifugation of the labelled granules showed the membrane label to be distributed largely between two peaks: one associated with intact granules and one with the characteristics of empty granule envelopes. Stimulation of hormones release in vitro led to the movement of membrane label from the intact granule fraction to the other one, consistent with the recapture of membrane as large vesicles. Freezing and thawing the crude granule fraction, ostensibly to aid osmotic fracture, produced a single membrane component with a density intermediate between the two original fractions.

Animals↗
PubMed1978

Preparation of antisera to three individual rat neurophysins and their use for radioimmunoassays.

A number of antisera have been raised against individual rat neurophysins. One of these proved suitable for the specific radioimmunoassay of rat vasopressin-neurophysin and data validating such a use are presented. Use of this antiserum showed that vasopressin-neurophysin is present in rat neurohypophyses in equimolar amounts to vasopressin, while in the hypothalamus the assay detected twice as much neurophysin-like material as hormone. A number of partially specific antisera for rat oxytocin-neurophysin have been obtained and the best of these was raised against the minor neurophysin.

Animals↗