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Biomedical subjects

L K Wainwright

Publications and source records attributed to L K Wainwright.

At least 37 records · Page 2Linked to original sources
PubMed1980

Regulation of the cycle in chick pineal serotonin N-acetyltransferase activity in vitro by light.

The diurnal cycle in vivo in the level of serotonin N-acetyltransferase (NAT) activity found in the pineal gland of chicks kept under diurnal lighting was reproduced in vitro with glands incubated in organ culture under the same diurnal lighting conditions. We have examined the effects of varying the lighting conditions of culture upon development of NAT activity in vitro with pineal glands from birds which were killed at different times during the photoperiod in vivo. The ability of chick pineal glands to develop increased NAT activity in culture during the dark period of a diurnal cycle of illumination was determined primarily by the proportion of the photoperiod in vivo elapsed at the time of sacrifice of the birds. The time of development of maximal NAT activity in cultured chick pineal glands could be advanced or delayed by corresponding changes in time of start of the dark period. However, the 'settings' of the pineal 'biological clock' remained unchanged. Glands from birds sacrificed in the final 30 min of the photoperiod in vivo developed increased NAT activity without lag when cultured in the light. Similarly, pineal glands cultured under continuous illumination developed an increased photostable NAT activity beginning at the time of the "subjective" end of the photoperiod in vitro. Ability to develop additional NAT activity in the dark was low rapidly at the "subjective" time in vitro of start of the next photoperoid. The maximal NAT activity developed in the dark consisted of both photolabile and photostable components.

Acetyltransferases↗
PubMed1979

Chick pineal serotonin acetyltransferase: a diurnal cycle maintained in vitro and its regulation by light.

We have reproduced in vitro the diurnal cycles in levels of serotonin acetyltransferase activity found in the chick pineal gland in vivo. The more closely the lighting conditions of culture matched those under which the birds were raised, the closer was the similarity between cycles in levels of enzyme activity in vitro and in vivo. Repetitive cycles in levels of acetyltransferase activity persisted in culture for at least 4 days under a diurnal cycle of illumination, and at least 2 days in continuous darkness. When glands were explanted into culture in the light phase of a cycle, short periods of further exposure to light markedly stimulated subsequent increase of acetyltransferase in the dark (after a short lag). Prolonged exposure to light in culture markedly inhibited increase of enzyme activity. Cycles in the levels of enzyme activity in glands cultured under altered light cycles were regulated primarily by changes in illumination. However, the endogenous biological 'clock' remained at least partly entrained to the original light cycle. Increase of acetyltransferase activity in vitro was markedly stimulated by theophylline plus compound Ro. 20.1724 (4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone) under all lighting conditions. Kinetics (to the time of attaining maximum levels in situ) of the increase under diurnal lighting and in constant darkness were indistinguishable from those in vivo. A high concentration of dl-propranolol markedly stimulated an increase in acetyltransferase activity in glands cultured in constant darkness but had little effect on glands under diurnal lighting or continuous illumination.

Acetyltransferases↗
PubMed1978

Preparation of cell populations with stabilized erythropoietic potential from the primitive streak chick blastodisc: some implications for control of gastrulation.

Improved methods for preparation from primitive streak chick blastodiscs of cell suspensions capable of forming erythroid cells in culture have been developed. When blastodiscs were preincubayed with hyaluronidase in the absence of collagenase before cell dispersion and a high concentration of methyl-alpha-mannoside was present in all media, the yields of cells were some 10-fold higher than those obtained by former procedures. Cell suspensions obtained consisted almost entirely of viable cells, yielded large numbers of free mature erythrocytes in liquid culture, and formed erythroid colonies and bursts in solidified medium. The capacity to form differentiated cells after resedimenrtation through Ficoll density gradients was partly stabilized. Addition of gee yolk homogenate to the blastodiscs immediately following treatment with hyaluronidase and to all media used thereafter largely stabilized the capacity to form erythroid cells during resedimentation through Ficoll density gradients. Possible relevance of observations made during development of the procedures to the control of onset of cell migration in the process of gastrulation is indicated.

Animals↗
PubMed1978

Regulation of the diurnal cycle in activity of serotonin acetyltransferase in the chick pineal gland.

When chick pineal glands were explanted into organ culture at midlight phase of a diurnal cycle of illumination and incubated in the dark, they developed marked increases in serotonin acetyltransferase (acetyl coA:arylamine N-acetyltransferase; EC 2.3.1.5) activity. Either this increase in activity was inhibited or its onset was retarded in glands incubated under constant illumination. Supplements of theophylline, isobutylmethylxanthine, quinidine, and compound Ro 20-1724 (4-(3-butoxyl-4-methoxybenzyl)-2-imidazolidinone) elicited very marked increases in serotonin acetyltransferase activity in glands cultured in the dark. Levels of activity attained after 6 h in culture approached or exceeded the maximum levels attained at middark phase of the diurnal cycle in vivo. Effects of theophylline and compound Ro 20-1724 were additive. Supplements of dibutryl cAMP had little or no effect upon levels of serotonin acetyltransferase activity when tested alone or in combination with theophylline but further enhanced the increase in the level of enzyme activity elicited by Ro 20-1724. Adenosine and cAMP had little or no effect upon levels of serotonin acetyltransferase activity. It is concluded that levels of serotonin acetyltransferase activity in the chick pineal gland are regulated by a repressive, negative-control mechanism, which probably involves a membranous adenosine receptor.

4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone↗
PubMed1976

Cellular composition of erythropoietic cell populations and aggregate cell cultures derived from early chick blastodiscs.

Light and electron microscopy of suspensions of cells prepared by dispersing chick blastodiscs at primitive-streak and head-fold stages showed the presence of numerous yolk granules, yolk-rich endodermal cells and occasional presumed ecto- and mesodermal cells. Several cell fractions prepared from this suspension by sedimentation through discontinuous Ficoll gradients were of similar composition. No enrichment of any particular cell type which might account for either differential sedimentation or erythropoietic potential of the fractions could be recognized. Two fractions, EP 1, and EP 2, were cultured as cell aggregates on vitelline membranes. EP 1 produced highly organized blood islands containing developing erythrocyte cells, organized endothelium, fibroblasts, thrombocytes and occasional granulocytes. Blood islands derived from EP 2, on the other hand, contained essentially only aggregates of erythroblasts embedded in endoderm. It is tentatively suggested that EP1 contains young multipotential hematopoietic precursors while EP 2 has only older blood-cell precursors committed to erythrocyte development. No cellular basis for the resolution of EP 1 into two complementary subfractions could be recognized.

Animals↗