Comparison of the time courses of luteinizing hormone (LH) secretion rates during continuous stimulation by LH-releasing hormone (LH-RH) in vivo and in vitro

Summary The patterns of LH secretion during constant stimulation of the pituitary glands of estradiol-treated ovariectomized rats with a maximally stimulating amount of LH-RH in vivo and in vitro correspond with each other qualitatively and quantitatively. In vitro the changes with time of the LH secretion rate are somewhat retarded, especially the occurrence of desensitization.     

Comparison of the time courses of luteinizing hormone (LH) secretion rates during continuous stimulation by LH-releasing hormone (LH-RH) in vivo and in vitro

The patterns of LH secretion during constant stimulation of the pituitary glands of estradiol-treated ovariectomized rats with a maximally stimulating amount of LH-RH in vivo and in vitro correspond with each other qualitatively and quantitatively. In vitro the changes with time of the LH secretion rate are somewhat retarded, especially the occurrence of desensitization.     

Studies on the modulation of the desensitization of the pituitary gland by luteinizing hormone-releasing hormone in the ovariectomized rat

In ovariectomized rats the desensitization of the LH cells in vivo, which develops during constant rate infusion of LHRH, 1) does not depend on a concomitant depletion of the pituitary LH stores, 2) proceeds normally when the hypothalamo-pituitary connection has been severed and 3) is a process in which LH itself is not involved.     

Studies on the modulation of the desensitization of the pituitary gland by luteinizing hormone-releasing hormone in the ovariectomized rat

Summary In ovariectomized rats the desensitization of the LH cells in vivo, which develops during constant rate infusion of LHRH, 1) does not depend on a concomitant depletion of the pituitary LH stores, 2) proceeds normally when the hypothalamo-pituitary connection has been severed and 3) is a process in which LH itself is not involved.     

Leydig cell function in streptozotocin-induced diabetic rats.

Streptozotocin diabetic rats were infertile as a result of decreased Leydig cell function of the testes. The major changes found were: decreased number of Leydig cells and their spontaneous secretion of testosterone. No change in the receptors to LH on the Leydig cells was observed. LH was found to be obligatory for the regulation of Leydig cell function and fertility.     

Leydig cell function in streptozotocin-induced diabetic rats

Summary Streptozotocin diabetic rats were infertile as a result of decreased Leydig cell function of the testes. The major changes found were: decreased number of Leydig cells and their spontaneous secretion of testosterone. No change in the receptors to LH on the Leydig cells was observed. LH was found to be obligatory for the regulation of Leydig cell function and fertility.     

Alzheimer’s disease: the impact of age-related changes in reproductive hormones

Receptors for hormones of the hypothalamic-pituitary-gonadal (HPG) axis that regulate reproductive function are expressed throughout the brain, and in particular the limbic system. The most studied of these hormones, the sex steroids, contain receptors throughout the brain, and numerous estrogenic, progestrogenic and androgenic effects have been reported in the brain related to development, maintenance and cognitive functions. Although less studied, receptors for gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) and activins also are found throughout the limbic system on a number of cell types, and they too transduce signals from circulating hormones as demonstrated by their multiple effects on the growth, development, maintenance and function of the brain. This review highlights the point that because of the feedback loops within the HPG axis, it is difficult to ascribe structural and functional changes during development, adulthood and senescence to a single HPG hormone, since a change in the concentration of any hormone in the axis will modulate hormone concentrations and/or receptor expression patterns for all other members of the axis. The most studied of these situations is the change in serum and neuronal concentrations of HPG hormones associated with menopause/andropause. Dysregulation of the HPG axis at this time results in increases in the concentrations of serum GnRH, gonadotropins and activins, decreases in the serum concentrations of sex steroid and inhibin, and increases in GnRH and LH receptor expression. Such changes would result in significantly altered neuronal signaling, with the final result being that there is i.e. increased neuronal GnRH, LH and activin signaling, but decreased sex steroid signaling. Therefore, loss of cognitive function during senescence, typically ascribed to sex steroids, may also result from increased signaling via GnRH, LH or activin receptors. Future studies will be required to differentiate which hormones of the HPG axis regulate/maintain cognitive function. This introductory review highlights the importance of the identification of HPG hormone neuronal receptors and the potential of serum HPG hormones to transduce signals to regulate brain structure and function during development and adult life.     

Effect of estrogens on LH- and FSH-levels in prepuberal male and female androgenized rats

Summary This paper has demonstrated that neonatal androgenization increases in prepuberal male and female rats the FSH-levels without changes in LH, indicating that the sexual differences in the control of FSH is a relevant process that takes place during the differentiation of the hypothalamus.Supported by a grant from the Consejo Nacional de Investigaciones Cientificas y Técnicas, Rep. Argentina.Acknowledgment. We are grateful to NIAMD, Rat Pituitary Program, for the reagents for the radioimmunoassays.     

Speed of in vitro reassociation of gonadotropin subunits in a teleost fish, the carp (Cyprinus carpio L.)]

Purified gonadotropin subunits of a teleost Fish, the Carp, reassociated in vitro, according to a second order rate reaction. The rate constant was temperature dependent. Compared to ovine LH, the Q10 was about three times less and the rate constant much greater (160 times for instance at 20 degrees C). The possible physiological significance of these differences is underlined.     

Luteinizing hormone content of the pars tuberalis of the hypophysis of neonatally androgenized female rats

Summary The immunoreactive LH content of the pars tuberalis of neonatally androgenized female rats was studied and found to be significantly lower than that of control females at oestrus or of control males. It is concluded that the rat pars tuberalis does secrete LH and that this secretory activity is diminished by neonatal androgenization in a manner that differs from that reported for the LH secretion in the pars distalis.This investigation received financial support from Direccion de Investigacion, grants RMS-80-13 and S-80-26, Universidad Austral de Chile.     

Etude ultrastructurale des variation cytologiques induites par la lumière sur l'adénohypophyse de la caille mâle

Summary The collective data obtained at the ultrastructural level in anterior pituitaries of male Chinese quails submitted to long daily photoperiods, confirm the cytological changes observed earlier in, at least, 2 types of cells of the gland. This cellular types may be the source of avain LH and FSH.     

Alloxan-induced hyperglycemia increases progestin and androgen accumulation by isolated rabbit follicles in vitro

Follicles isolated from Alloxan-treated rabbits and incubated in vitro, accumulated more progesterone and testosterone than those from saline-treated rabbits. LH augmented the accumulation of these 2 steroids. By contrast, the estradiol response to LH stimulation by follicles from Alloxan-induced hyperglycemic rabbits was diminished when compared to follicles from saline-treated rabbits. Ovaries from hyperglycemic rabbits also appeared to have more cystic follicles.     

Effects of a bovine pineal peptidic fraction (E5) on plasma and pituitary levels of LH,FSH and prolactin

Summary Pituitary levels of prolactin were significantly diminished after 5 s.c. injections spaced 12 h apart of 5 g of a partially purified bovine pineal peptide fraction (E₅) in both intact and castrated rats. E₅ treatment did not significantly affect the castration-induced changes in plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH) or pituitary LH but did partially block the pituitary fall in FSH in castrated animals.Supported by NSF grant PCM 8003441 and NIH Center for Reproductive Biology (Bioassay Core) No.P30 HD 10202. Many thanks are due A. Moreno for his excellent technical assistance.     

Hyperprolactinemia and estrogen-induced rhythms in LH and prolactin release in the ovariectomized rat

Short-term (9 days) hyperprolactinemia induced by pituitary grafts reduced basal plasma LH levels in ovariectomized rats whereas long-term (31 days) grafts increased basal LH levels. Although long-term grafts inhibited estradiol-induced prolactin surges, hyperprolactinemia had no effect on the LH surge. It is concluded that the estrogen-treated ovariectomized rat is not suitable for studying the effects of hyperprolactinemia on LH release.     

Release of immuno-reactive and biologically active LH from fetal mouse pituitary in response to synthetic gonadotropin releasing factor (LRF).

In an incubation system, LRF stimulated significantly the release of LH from 18-day-old mouse fetal pituitary. This LRF-induced LH release, measured by RIA in the incubation medium was able to increase the testosterone production by age-matched fetal testes. This data suggests that the hypothalamo-hypophyseal-testicular axis is functional at the end of mouse prenatal life.     

Rate of tryptophan hydroxylation in vivo in brain nuclei of genetically hypertensive rats of the Lyon strain

The rate of tryptophan hydroxylation in vivo is unaltered in brain areas of 5, 9 and 21 week-old Lyon genetically Hypertensive (LH) rats as compared to both Lyon Normotensive (LN) and Low Blood Pressure (LL) rats, except for a decrease in the C1 area of the medulla oblongata in 9 week-old animals.     

商用车ABS预测控制方法研究

针对商用车制动过程中存在的强烈非线性和模型不确定性问题,建立了整车七自由度转向制动状态空间模型,提出了一种非线性连续预测控制方法,设计了基于滑移率的ABS非线性预测控制器.在控制器设计中,利用泰勒级数展开对系统状态进行适当的截尾处理,获得了系统预测模型,并将ABS路面识别算法引入参考轨迹设计,提出了多路面下的参考轨迹模型.当路况发生变化时,参考轨迹也发生相应的变化,而且在系统中引入了积分反馈,以增强系统的鲁棒性.仿真研究表明,当ABS存在建模误差、载荷变化和干扰时,该非线性预测控制器仍能够获得良好的动态响应和鲁棒性.     

Hyperprolactinemia and estrogen-induced rhythms in LH and prolactin release in the ovariectomized rat

Summary Short-term (9 days) hyperprolactinemia induced by pituitary grafts reduced basal plasma LH levels in ovariectomized rats whereas long-term (31 days) grafts increased basal LH levels. Although long-term grafts inhibited estradiol-induced prolactin surges, hyperprolactinemia had no effect on the LH surge. It is concluded that the estrogen-treated ovariectomized rat is not suitable for studying the effects of hyperprolactinemia on LH release.     

Alloxan-induced hyperglycemia increases progestin and androgen accumulation by isolated rabbit follicles in vitro

Summary Follicles isolated from Alloxan-treated rabbits and incubated in vitro, accumulated more progesterone and testosterone than those from saline-treated rabbits. LH augmented the accumulation of these 2 steroids. By contrast, the estradiol response to LH stimulation by follicles from Alloxan-induced hyperglycemic rabbits was diminished when compared to follicles from saline-treated rabbits. Ovaries from hyperglycemic rabbits also appeared to have more cystic follicles.This work was supported by the Medical Research Council of Canada. The technical assistance of Misses P. Dimond and J. Osoko is gratefully acknowledged. Dr B.R. Bhavnani provided the stimulus for this study.     

The effect of gonadotrophins on the steroidogenesis, in the ovary and testis of gonadotrophin-deprived fresh water teleost, Cyprinus carpio.

Studies have been made on the effect of LH, FSH, and LH+FSH on the gonadal steroidogenesis in gonadotrophin-deprived common carp. LH alone and in combination with FSH was more effective than FSH in stimulation of steroidogenesis.