PHOTOPERIODIC CONTROL OF LH RELEASE IN THE RAM

1975 ◽  
Vol 78 (3) ◽  
pp. 435-441 ◽  
Author(s):  
J. Pelletier ◽  
R. Ortavant
Keyword(s):  
Sharp Increase ◽  
Photoperiodic Control ◽  
Slow Decline ◽  
Lh Release ◽  
Light Rhythm

ABSTRACT The influence of variations in the duration of light photoperiod on LH release has been studied in intact and castrated rams submitted to a 6 months "annual" light rhythm. Blood was collected once a month and the plasma LH levels were determined by radioimmunoassay. In intact rams, the LH level is decreased when the light photoperiod is increased, but as soon as this photoperiod begins to decrease, a sharp increase (about 80%) in the LH level is observed. Thereafter a slow decline in plasma LH occurs until the photoperiod reaches a minimum. In the castrated animals, the plasma LH level is three to four times higher than in the intact animals but the pattern of the variations with regard to the light photoperiod duration, is essentially the same. Thus an increase of 59 and 43 % in plasma LH occurs in the two breeds used when the light photoperiod begins to decrease. These results indicate that hypothalamo-hypophyseal activity is modulated by gradual changes in the duration of light photoperiods either in the presence or absence of androgens.

Mechanisms of action of testosterone propionate on LH and FSH release by the pituitary gland in cyclic female rats

1980 ◽  
Vol 95 (2) ◽  
pp. 158-165 ◽  
Author(s):  
J. Roos ◽  
S. Plas-Roser ◽  
Cl. Aron
Keyword(s):  
Pituitary Gland ◽  
Sharp Increase ◽  
Testosterone Propionate ◽  
Sharp Decrease ◽  
Mechanisms Of Action ◽  
The Other ◽  
Female Rats ◽  
Corpora Lutea ◽  
Other Hand ◽  
Lh Release

Abstract. The aim of this work was to determine whether changes in pituitary responsiveness to LRH could account for the effect of testosterone propionate (TP) on the gonadotrophic function of the pituitary in 4-day cyclic female rats. Doses of 250, 500 and 1000 ng LRH were injected ip on pro-oestrus at 15.30 h in rats either pre-treated with 5 mg TP on dioestrus II at 10.00 h or injected with 30 mg/kg pentobarbital (PB) at 13.00 h. LH release induced within 30 min by LRH was higher in PB than in TP-treated rats. Even by using 250 ng LRH full ovulation was observed on the morning of oestrus in PB-treated rats. On the other hand, only partial ovulation occurred whatever the dose of LRH used in TP-treated rats; a great number of luteinized follicles was shown to be constantly associated with post-ovulatory corpora lutea. While LRH caused a significant FSH release (30 min later) in TP-treated rats, no FSH release could be shown in PB-treated rats. The pituitary FSH content appeared to be decreased and the pituitary LH content remained unchanged while a sharp increase in both blood FSH and LH concentrations occurred following injection of 1000 ng LRH in TP-treated rats. Concomitantly a sharp decrease in the number of pituitary gonadotrophs (AB-PAS+) was observed. A significant decrease in the number of the small roundshaped PAS positive cells was also observed. The mechanisms whereby TP influences the function of the pituitary-ovarian axis are discussed in the light of these results.

Photoperiodic control of cytokinin transport and metabolism in Chenopodium rubrum

1996 ◽  
Vol 98 (3) ◽  
pp. 564-570 ◽  
Author(s):  
Ivana Machackova ◽  
Josef Eder ◽  
Vaclav Motyka ◽  
Jan Hanus ◽  
Jan Krekule
Keyword(s):  
Chenopodium Rubrum ◽  
Photoperiodic Control

Prostanoid Release from Ex Vivo Perfused Canine Arteries and Veins: Effects of Prolonged Perfusion, Intermittent Perfusion, as well as Exposure to Exogenous Arachidonic Acid, Thrombin and Bradykinin

1989 ◽  
Vol 62 (03) ◽  
pp. 1034-1039 ◽  
Author(s):  
Jan S Brunkwall ◽  
James C Stanley ◽  
Timothy F Kresowik ◽  
Linda M Graham ◽  
William E Burkel ◽  
...  
Keyword(s):  
Arachidonic Acid ◽  
Ex Vivo ◽  
Fold Increase ◽  
Ex Vivo Perfusion ◽  
Cyclooxygenase Activity ◽  
Perfusion Model ◽  
Prostanoid Production ◽  
Slow Decline ◽  
Arteries And Veins ◽  
Nonpulsatile Flow

SummaryRegulation of prostanoid release from ex vivo perfused vessel segments is not fully understood. A series of perfusion experiments were performed with canine arteries and veins to define certain regulatory phenomena. Arteries were perfused with pulsatile flow of 90 ml/min at a pressure of 100 mmHg, and veins with nonpulsatile flow of 90 ml/min at a pressure of 7 mmHg. Segments were perfused with Hanks' balanced salt solution for five 15-min periods with the perfusate exchanged after each study period. With onset of perfusion, there was an initial burst of prostacyclin release to 127 ± 40 pg/mm2, declining to 32 ± 10 pg/mm2 after 60 minutes (p <0.005). If perfusion continued for 5.5 hours, there was a stable release period between 1 and 3 hours, followed by a very slow decline. At that time addition of arachidonic acid (AA) increased prostacyclin release six-fold (p <0.01). Vessels perfused for 1 hour and then rested for another hour, responded to reperfusion at the second onset of flow with a two-fold increase in prostacyclin release (p <0.01). Vessels perfused with thrombin, bradykinin or A A (either added to each perfusate or only to the last perfusate) exhibited greater prostacyclin release than did control segments. Release of thromboxane steadily declined with time in all parts of the study, and only increased with the addition of A A to the perfusate. These data indicate that vessel segments subjected to ex vivo perfusion do not maximally utilize enzyme systems responsible for prostanoid production, and after 1 hour perfusion have not depleted their phospholipids, and maintain functioning levels of phospholipase and cyclooxygenase activity. This perfusion model allows for the study of prostacyclin and thromboxane release from arteries and veins and their response to various drugs and other stimuli.

World Economic Crisis as a Process of Substitution of Technological Modes

2009 ◽  
pp. 26-38 ◽  
Author(s):  
S. Glaziev
Keyword(s):  
Economic Crisis ◽  
Economic Activity ◽  
Sharp Increase ◽  
Energy Resources ◽  
Long Wave ◽  
The World ◽  
World Economic ◽  
Technological Mode ◽  
World Economic Crisis

The article analyzes fundamental reasons for the world economic crisis in the light of global technological shifts. It proves that it is caused by the substitution of technological modes. It is shown that sharp increase and slump in stock indices and prices for energy resources are typical of the process of technological substitution which occurs regularly according to the rhythm of long-wave fluctuations of the world economic activity. The article rationalizes a package of anti-crisis measures aimed at stimulating the new technological mode. Its structure and role of the locomotive factor of the new long wave of economic growth are revealed.

Monitoring land use change in the Lake Taupo catchment between 1975, 1990 and 2002 using satellite remote sensing data

2007 ◽  
pp. 17-22
Author(s):  
H. Lilienthal ◽  
A. Brauer ◽  
K. Betteridge ◽  
E. Schnug
Keyword(s):  
Remote Sensing ◽  
Water Quality ◽  
Land Use ◽  
Land Use Change ◽  
Satellite Remote Sensing ◽  
Remote Sensing Data ◽  
Native Vegetation ◽  
Lake Water Quality ◽  
Livestock Farming ◽  
Slow Decline

Conversion of native vegetation into farmed grassland in the Lake Taupo catchment commenced in the late 1950s. The lake's iconic value is being threatened by the slow decline in lake water quality that has become apparent since the 1970s. Keywords: satellite remote sensing, nitrate leaching, land use change, livestock farming, land management

Androgenic and oestrogenic steroid participation in feedback control of luteinizing hormone secretion in male sheep

1983 ◽  
Vol 102 (4) ◽  
pp. 499-504 ◽  
Author(s):  
M. J. D'Occhio ◽  
B. D. Schanbacher ◽  
J. E. Kinder
Keyword(s):  
Luteinizing Hormone ◽  
Pulse Generator ◽  
Hormone Secretion ◽  
Pulse Interval ◽  
Serum Concentrations ◽  
Luteinizing Hormone Secretion ◽  
Lh Release ◽  
Lh Secretion ◽  
Additional Feedback ◽  
Male Sheep

Abstract. The acute castrate ram (wether) was used as an experimental model to investigate the site(s) of feedback on luteinizing hormone (LH) by testosterone, dihydrotestosterone and oestradiol. At the time of castration, wethers were implanted subdermally with Silastic capsules containing either crystalline testosterone (three 30 cm capsules), dihydrotestosterone (five 30 cm capsules) or oestradiol (one 6.5 cm capsule). Blood samples were taken at 10 min intervals for 6 h 2 weeks after implantation to determine serum steroid concentrations and to characterize the patterns of LH secretion. Pituitary LH response to exogenous LRH (5 ng/kg body weight) were also determined at the same time. The steroid implants produced serum concentrations of the respective hormones which were either one-third (testosterone) or two-to-four times (dihydrotestosterone, oestradiol) the levels measured in rams at the time of castration. Non-implanted wethers showed rhythmic pulses of LH (pulse interval 40–60 min) and had elevated LH levels (16.1 ± 1.6 ng/ml; mean ± se) 2 weeks after castration. All three steroids suppressed pulsatile LH release and reduced mean LH levels (to below 3 ng/ml) and pituitary LH responses to LRH. Inhibition of pulsatile LH secretion by all three steroids indicated that testosterone as well as its androgenic and oestrogenic metabolites can inhibit the LRH pulse generator in the hypothalamus. Additional feedback on the pituitary was indicated by the dampened LH responses to exogenous LRH.

TRH stimulates LH release in adolescents with delayed puberty

1986 ◽  
Vol 113 (1_Suppl) ◽  
pp. S33-S34
Author(s):  
W.D. HETZEL ◽  
U. SIEBLING ◽  
L. ABERLE
Keyword(s):  
Delayed Puberty ◽  
Lh Release
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