THE ACTION OF SOME OVULATION INHIBITORS ON THE RABBIT HYPOTHALAMUS

1971 ◽  
Vol 66 (2) ◽  
pp. 221-228 ◽  
Author(s):  
Dona A. Frith ◽  
K. C. Hooper
Keyword(s):  
Enzyme Activity ◽  
Hormone Secretion ◽  
Chlormadinone Acetate ◽  
Releasing Factors ◽  
Sites Of Action ◽  
Ethinyl Oestradiol

ABSTRACT The previous paper (Frith & Hooper 1971) described the activities of certain hypothalamic enzymes at various times after mating and it was suggested that changes in enzymes levels may be used as an index of the release of gonadotrophic hormones. Using this approach, a study has been made of the action of the ovulation inhibitors chlormadinone acetate, norethindrone, ethinyl oestradiol and oestrone on the rabbit hypothalamus. The four inhibitors increased enzyme activity in the hypothalamus. Previous work has shown that raised levels of enzyme activity are associated with a lowered level of gonadotrophic hormone secretion. It is suggested, therefore, that one of the sites of action of the inhibitors is on polypeptide turnover in the hypothalamus, and it seems possible that this is one of the factors controlling the availability of gonadotrophin releasing factors.

Effects of human pancreatic and rat hypothalamic growth hormone-releasing factors on growth hormone secretion in steers

1986 ◽  
Vol 3 (2) ◽  
pp. 87-94 ◽  
Author(s):  
S.N. Al-Raheem ◽  
J.E. Wheaton ◽  
Y.G. Massri ◽  
J.M. Marcek ◽  
R.D. Goodrich ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Hormone Secretion ◽  
Growth Hormone Secretion ◽  
Releasing Factors

In-vitro control of growth hormone secretion by synthetic releasing factors in young and adult ducks (Anas platyrhynchos)

1988 ◽  
Vol 119 (3) ◽  
pp. 421-429 ◽  
Author(s):  
C. Foltzer-Jourdainne ◽  
S. Harvey ◽  
P. Mialhe
Keyword(s):  
Low Dose ◽  
Hormone Secretion ◽  
Growth Hormone Secretion ◽  
Age Related ◽  
Basal Release ◽  
Pituitary Glands ◽  
Releasing Factors ◽  
Somatostatin 14

ABSTRACT Release of GH from perifused duckling hemipituitaries was stimulated, in a biphasic manner, by synthetic TRH and human pancreatic GH-releasing factor (GRF). At all effective concentrations, the level of GH release was increased within 5 min of TRH or GRF perifusion and was maximal after 10 min of TRH perifusion and after 20 min of GRF perifusion. Although TRH was perifused for 20 min the level of GH release declined during the last 10 min. The most effective dose of TRH (1·0 μg/ml; 2·7 μmol/l) and GRF (0·5 μg/ml; 110 nmol/l) provoked similar (250– 300%) increases in the level of GH release. However, since the effect of TRH was only of short duration, the total release of GH induced by GRF was higher than that elicited by TRH, especially with the low dose. The increase in release of GH induced by TRH or GRF was blunted when pituitaries from adult ducks were used. As in young ducks, the GH response to GRF was higher, whereas the response to TRH was very low. The GH response of perifused adult pituitaries to GRF was, however, potentiated when TRH was perifused simultaneously. The basal release of GH from both young and adult pituitary glands was unaffected by perifusion with somatostatin-14 (SRIF-14) at doses of 1 and 2 μg/ml. The perifusion of hemipituitary glands with similar doses of SRIF-14 was also unable to suppress the stimulation of GH release induced by prior perifusion with GRF, although when SRIF-14 and TRH were simultaneously perifused TRH-induced GH release was markedly suppressed. These results demonstrate direct effects and interactions of TRH, GRF and SRIF on the release of GH from duck pituitary glands. GRF is the most potent releasing factor for GH in both young and adult ducks although in adult ducks it is less effective. These results also provide evidence that the age-related decline in the in-vivo GH response to TRH is due to a desensitization of pituitary somatotrophs. J. Endocr. (1988) 119, 421–429

scholarly journals Growth hormone secretion in Turner's syndrome and influence of oxandrolone and ethinyl oestradiol.

1989 ◽  
Vol 64 (4) ◽  
pp. 587-592 ◽  
Author(s):  
A A Massarano ◽  
C G Brook ◽  
P C Hindmarsh ◽  
P J Pringle ◽  
J D Teale ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Hormone Secretion ◽  
Growth Hormone Secretion ◽  
Turner's Syndrome ◽  
Turner’S Syndrome ◽  
Ethinyl Oestradiol

scholarly journals Point Mutations as Main Resistance Mechanism Together With P450-Based Metabolism Confer Broad Resistance to Different ALS-Inhibiting Herbicides in Glebionis coronaria From Tunisia

2021 ◽  
Vol 12 ◽  
Author(s):  
Zeineb Hada ◽  
Yosra Menchari ◽  
Antonia M. Rojano-Delgado ◽  
Joel Torra ◽  
Julio Menéndez ◽  
...  
Keyword(s):  
Enzyme Activity ◽  
Dose Response ◽  
Resistance Mechanism ◽  
Point Mutations ◽  
Acetolactate Synthase ◽  
Target Site ◽  
Cross Resistance ◽  
P450 Monooxygenase ◽  
Target Site Resistance ◽  
Sites Of Action

Resistance to acetolactate synthase (ALS) inhibiting herbicides has recently been reported in Glebionis coronaria from wheat fields in northern Tunisia, where the weed is widespread. However, potential resistance mechanisms conferring resistance in these populations are unknown. The aim of this research was to study target-site resistance (TSR) and non-target-site resistance (NTSR) mechanisms present in two putative resistant (R) populations. Dose–response experiments, ALS enzyme activity assays, ALS gene sequencing, absorption and translocation experiments with radiolabeled herbicides, and metabolism experiments were carried out for this purpose. Whole plant trials confirmed high resistance levels to tribenuron and cross-resistance to florasulam and imazamox. ALS enzyme activity further confirmed cross-resistance to these three herbicides and also to bispyribac, but not to flucarbazone. Sequence analysis revealed the presence of amino acid substitutions in positions 197, 376, and 574 of the target enzyme. Among the NTSR mechanisms investigated, absorption or translocation did not contribute to resistance, while evidences of the presence of enhanced metabolism were provided. A pretreatment with the cytochrome P450 monooxygenase (P450) inhibitor malathion partially synergized with imazamox in post-emergence but not with tribenuron in dose–response experiments. Additionally, an imazamox hydroxyl metabolite was detected in both R populations in metabolism experiments, which disappeared with the pretreatment with malathion. This study confirms the evolution of cross-resistance to ALS inhibiting herbicides in G. coronaria from Tunisia through TSR and NTSR mechanisms. The presence of enhanced metabolism involving P450 is threatening the chemical management of this weed in Tunisian wheat fields, since it might confer cross-resistance to other sites of action.

Regulation of cholecystokinin secretion by intraluminal releasing factors

1995 ◽  
Vol 269 (3) ◽  
pp. G319-G327 ◽  
Author(s):  
R. A. Liddle
Keyword(s):  
Small Intestine ◽  
Hormone Secretion ◽  
Gastrointestinal Hormones ◽  
Chemical Characterization ◽  
Pancreatic Acinar Cells ◽  
Gallbladder Contraction ◽  
Proximal Small Intestine ◽  
Releasing Factors ◽  
Contraction Regulation ◽  
Stimulation Of

Ingested nutrients stimulate secretion of gastrointestinal hormones that are necessary for the coordinated processes of digestion and absorption of food. One of the most important hormonal regulators of the digestive process is cholecystokinin (CCK). This hormone is concentrated in the proximal small intestine and is secreted into the blood on the ingestion of proteins and fats. The physiological actions of CCK include stimulation of pancreatic secretion and gallbladder contraction, regulation of gastric emptying, and induction of satiety. Therefore, in a highly coordinated manner CCK regulates the ingestion, digestion, and absorption of nutrients. The manner by which foods affect enteric hormone secretion is largely unknown. However, it has recently become apparent that two CCK-releasing factors are present in the lumen of the proximal small intestine. One of these factors, known as monitor peptide, has been chemically characterized. Monitor peptide is produced by pancreatic acinar cells and is secreted by way of the pancreatic duct into the duodenum. On reaching the small intestine, monitor peptide interacts with CCK cells to induce hormone secretion. A CCK-releasing factor of intestinal origin has been partially characterized and is responsible for stimulation of CCK secretion after 1) ingestion of protein or fats, 2) instillation of protease inhibitors into the duodenum, or 3) diversion of bile-pancreatic juice from the upper small intestine. Together, these releasing factors provide positive and negative feedback mechanisms for regulation of CCK secretion. This review discusses the physiological observations that have led to the chemical characterization of the CCK-releasing factors and the potential implications of this work to other hormones of the gastrointestinal tract.

scholarly journals Peroxidase and peroxidase-oxidase activities of isolated human myeloperoxidases

1987 ◽  
Vol 242 (3) ◽  
pp. 673-680 ◽  
Author(s):  
B E Svensson ◽  
K Domeij ◽  
S Lindvall ◽  
G Rydell
Keyword(s):  
Enzyme Activity ◽  
Cation Exchange ◽  
Gel Filtration ◽  
Exchange Chromatography ◽  
Relative Molecular Mass ◽  
Cation Exchange Chromatography ◽  
Healthy Donors ◽  
Activity Measurements ◽  
Molecular Masses ◽  
Sites Of Action

Isolated neutrophils from healthy donors were used for the isolation of four highly purified forms of myeloperoxidase as determined by spectral (A430/A280 ratio 0.80-0.87) and enzyme-activity measurements. Although the myeloperoxidases exhibited different elution profiles on cation-exchange chromatography, gel filtration indicated similar relative molecular masses. When these forms were assayed for peroxidase and peroxidase-oxidase activities with several substrates, they all exhibited virtually the same specific activities. These results suggest that possible functional differences between the enzymes may be related to differences in their sites of action rather than to differences in enzyme activity. Myeloperoxidase from a patient with chronic myeloid leukaemia also revealed a similar heterogeneity on cation-exchange chromatography. However, this myeloperoxidase contained in addition one form with a lower and one form with a higher relative molecular mass, as indicated by gel-filtration chromatography.

scholarly journals Effects of WY-14643 on Peroxisomal Enzyme Activity and Hormone Secretion in Immortalized Human Trophoblast Cells

2009 ◽  
Vol 32 (7) ◽  
pp. 1278-1282
Author(s):  
Fumie Hashimoto ◽  
Mieko Morita ◽  
Kaori Iwasaki ◽  
Satoru Takeda ◽  
Hidenori Hayashi
Keyword(s):  
Enzyme Activity ◽  
Hormone Secretion ◽  
Trophoblast Cells ◽  
Peroxisomal Enzyme ◽  
Human Trophoblast ◽  
Human Trophoblast Cells

scholarly journals Short-Day Effects of Melatonin on Luteinizing Hormone Secretion in the Ewe: Evidence for Central Sites of Action in the Mediobasal Hypothalamus1

1993 ◽  
Vol 48 (4) ◽  
pp. 752-760 ◽  
Author(s):  
Benoit Malpaux ◽  
Agnes Daveau ◽  
Françoise Maurice ◽  
Veronique Gayrard ◽  
Jean-Claude Thiery
Keyword(s):  
Luteinizing Hormone ◽  
Hormone Secretion ◽  
Luteinizing Hormone Secretion ◽  
Short Day ◽  
Sites Of Action

THE ACTION OF PROGESTATIONAL AGENTS ON OXYTOCINASE ACTIVITY IN THE FEMALE RABBIT HYPOTHALAMUS

1972 ◽  
Vol 70 (3) ◽  
pp. 429-437
Author(s):  
Dona A. Frith ◽  
K. C. Hooper
Keyword(s):  
Enzyme Activity ◽  
Hormone Secretion ◽  
Female Rabbit ◽  
Activity Of Enzymes ◽  
Dose Levels

ABSTRACT Female rabbits were injected with progesterone, 20α-hydroxy-pregn-4-en-3-one (20α-OH) and 20β-hydroxy-pregn-4-en-3-one (20β-OH), and the effects of these progestogens on the activity of enzymes in the hypothalamus were noted. 20α-OH produced a significant decrease in enzyme activity whereas 20β-OH did not. It is suggested therefore that 20α-OH is responsible for the depression in enzyme activity which occurs in the female rabbit after coitus (Frith & Hooper 1971a). Progesterone, at different dose levels, produced effects on enzyme activity which can be correlated with the known pattern of gonadotrophic hormone secretion. The results substantiate the hypothesis proposed by the authors that there is a relationship between enzyme levels in the hypothalamus and gonadotrophic hormone secretion.

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