Effect of neonatal castration on the content of hypothalamic LHRH, pituitary LH and plasma LH in developing male rats.

The content of hypothalamic LHRH and concentration of LH in pituitary and plasma were measured on day 5, 7, 10, 14, 17, 22, 25, 30, 45, 52 and 60 in male rats which were bilaterally castrated on day 2. The levels of plasma LH were significantly higher in all the groups of castrated rats than in normal male rats of corresponding ages. The concentration of plasma LH did not rise progressively but showed day to day fluctuation apparently due to alteration of sexual differentiation of the hypothalamus. The concentration of pituitary LH was significantly lower in neonatally castrated rats compared to normal male rats except on days 17, 25 and 30. The content of hypothalamic LHRH declined initially following castration, but from day 17 onwards significantly higher levels of hypothalamic LHRH were maintained in neonatally castrated rats than in intact control. Initial decline in the content of hypothalamic LHRH may be because of stimulation of release of LHRH which exceeds maximal rate of synthesis and subsequent increase in the content of hypothalamic LHRH may be due to enhanced LHRH synthesis as a result of castration.     

Kinetic and autoradiographic studies on binding of hCG to the testicular LH receptors of neonatal rats

The properties of hCG binding to LH receptors of the neonatal (5-day-old) rat testis were analysed and compared with those of the adult testis. The equilibrium association constants (Ka) of hCG-binding were similar at both ages, 2-4 X 10(10) M-1. In contrast, kinetic binding studies revealed that the association and dissociation rate constants of hCG binding were more rapid in the neonatal testis. Likewise, it was observed that the progression from loose (easily dissociable) to tight (non-dissociable) binding was less complete in the young than in the adult testis. Autoradiography of 125I-labelled hCG binding to interstitial cell suspensions at the two ages showed that the gonadotrophin binding per Leydig cell was about 50% lower in the neonatal testis. Conversely, since the surface area of adult Leydig cells was about 4-fold larger, the receptor density appeared to be higher in the neonatal Leydig cells. The rapid recovery of LH receptors after hCG stimulation, typical of the neonatal cells, was due to rapid replenishment of binding in the cells initially occupied by the injected hormone, rather than to an hCG-induced increase of Leydig cell number. Finally, in-vivo experiments with cycloheximide revealed that the rapid recovery of LH receptors was dependent on protein synthesis. These differences in the kinetics of neonatal testicular LH receptor turnover may be involved in the unique functional features of the fetal-neonatal growth phase of rat testicular Leydig cells.     

Reversal of the unresponsiveness of neonatal rat ovary to LH in cAMP synthesis by estrogen.

The rat ovary during the 1st postnatal week is unresponsive to luteinizing hormone (LH), but responds to prostaglandin E1 with increase of cyclic adenosine 3',5'-monophosphate synthesis. In the present experiments unresponsiveness of ovaries of 6-day-old rats to LH in synthesis of cAMP was effectively reversed by injection of depot estradiol and diethylstilbestrol on the 2nd and 4th postnatal day. Administration of testosterone, progesterone, deoxycorticosterone, pregnant mare's serum gonadotropin and human chronic gonadotropin had no stimulatory effect. The lack of response to LH also failed to be reversed when estradiol was injected 21 h before killing of the animals or the ovaries were preincubated with estradiol. These results suggest that the development of an ovarian cell system responsive to LH in newborn rat may be accelerated by long-term action of estradiol.     

Comparative immunocytochemical demonstration of ACTH-, LH and FSH-containing cells in the pituitary of neonatal,immature and adult rats

Summary By means of immunocytochemistry, the development of ACTH-, LH- and FSH cells was examined in the anterior pituitary of 5-day-old neonatal, 15-day-old immature and adult rats. ACTH-positive cells are angular and the periphery of these cells is strongly reactive with anti-ACTH serum. In contrast, LH- and FSH-immunopositive cells are ovoid elements, ranging in cell size and intensity of staining. Angular cells, in which only the cell periphery reacted with anti-LH serum, were observed in neonatal and immature rats; however, these cells were not stained with either anti-FSH serum or anti-ACTH serum. Observation of serial semithin sections revealed that ACTH-immunopositive cells do not react with either anti-LH or anti-FSH serum. Finally, it was observed that ACTH cells and LH cells are both functionally differentiated already in 5-day-old neonatal rats.     

A correlative radioimmunoassay and immunohistochemical study of LHRH-induced LH depletion in the anterior pituitary of male and female neonatal rats in vitro

Summary After an exposure of 24 h to synthetic LHRH (100 ng/ml) in vitro, the anterior pituitaries of 4-day-old rats show a notable loss of immunoreactive material in most LH cells in males, but not in females. When radioimmunoassayed without incubation, the pituitary LH content of 4-day-old female rats is 2.8 times higher than that of males of the same age. LHRH treatment stimulates a higher rate of LH discharge in females than in males, but if LH release is expressed as a percentage of the initial pituitary LH content, there is no apparent difference. In both sexes, more than 70% of the initially stored LH is discharged into the medium after 24 h of LHRH stimulation. In males, this discharge produces a pronounced depletion, but in females, the pituitary still contains 78.2% of the initial LH content despite the large amount of hormone released.From these results, it is concluded that in newborn rats the LH synthetic rate in females is higher than that in males. This high synthetic activity, together with the large store of LH, may explain why prolonged LHRH treatment fails to cause LH depletion in females. At 4 days of age LHRH had no stimulatory effect on pituitary synthesis of LH in either sex.     

Controlling interrelationships of progesterone/LH and estradiol/LH in mares

The interrelationships of progesterone, estradiol, and LH were studied in mares (n=9), beginning at the first ovulation (Day 0) of an interovulatory interval. An increase in mean progesterone concentrations began on Day 0 and reached maximum on Day 6, with luteolysis beginning on Day 14. A common progesterone threshold concentration of about 2 ng/ml for a negative effect on LH occurred at the beginning and end of the luteal phase. Progesterone and LH concentrations decreased at a similar rate from Day 6 until the onset of luteolysis on Day 14, consistent with a decreasing positive effect of LH on progesterone. Concentrations of LH during the increase in the ovulatory surge consisted of two linear regression segments involving a rate of 0.4 ng/ml/day for Days 14-22 and 1.8 ng/ml/day for Day 22 to 1 day after the second ovulation. The end of the first segment and beginning of the second segment was 2 days before ovulation and was the day the ovulatory estradiol surge was at a peak.     

Role of LH in luteolysis and growth of the ovulatory follicle and estradiol regulation of LH secretion in heifers

The role of LH in luteolysis and development of the ovulatory follicle and the involvement of GnRH receptors in estradiol (E2) stimulation of LH secretion were studied in heifers. A pulse of PGF_2α, as indicated by a metabolite, was induced by E2 treatment on Day 15 (Day 0 = ovulation) and LH concentration was reduced with a GnRH-receptor antagonist (acyline) on Days 15, 16, and 17. Blood samples were collected every 6 h on Days 14-17 and hourly for 10 h beginning at the Day-15 treatments. Four groups were used (n = 6): control, acyline, E2, and E2/acyline. The number of LH pulses/heifer during the 10 h posttreatment was greater (P < 0.0002) in the E2 group (2.3 ± 0.4, mean ± SEM) than in the acyline group (0.2 ± 0.2) and was intermediate in the E2/acyline group (1.4 ± 0.2). Concentrations of progesterone in samples collected every 6 h on Day 15 showed a group-by-hour interaction (P < 0.02); concentrations decreased in the acyline group but not in the control group. The 12 heifers in the combined acyline and E2/acyline groups had three follicular waves compared to two waves in 10 of 12 heifers in the combined control and E2 groups. Results (1) supported the hypothesis that LH delays the progesterone decrease associated with luteolysis, (2) supported the hypothesis that LH has a positive effect on the continued development and growth of the selected ovulatory follicle, and (3) indicated that E2 stimulates LH production through an intracellular pathway that involves GnRH receptors on the gonadotropes and a pathway that does not involve the receptors.     

Temporal relationship of the prolactin-dependent LH-induced LH receptor to the LH stimulus

The time course for LH induction of luteinizing hormone (LH) receptors as reflected in binding of ¹²⁵l-labeled hCG was investigated in hypophysecto-mized adult male rats. A low dose of oLH (10 μg) was administered to hypophysectomized adult male rats following pretreatments with prolactin, follicle-stimulating hormone (FSH), growth hormone (GH), or saline. Testicular binding of hCG was determined at different times following the LH injection using Leydig cell membrane preparations from a testicular homogenate. Seven days after hypophysectomy, hCG binding was at a nadir of 19 ± 7% (mean ± SD) of control values. Pretreatment with prolactin (100 μg/day) for 7 days was associated with a nonsignificantly different hCG binding that was 30 ± 5% of control values. Prolactin pretreatment plus a single 10 μg LH i.p. injection increased ¹²⁵l hCG binding up to 56 ± 10% of control values within 30 minutes of the LH injection. Luteinizing hormone-induced hCG binding persisted at a high level (51 ± 4% of control values) for 2 hours but returned to hypophysectomized control levels 6 hours after the i.p. LH injection. Seven days pretreatment with FSH or GH at 100 μg/day plus 10-μg LH injections was also tested. Neither FSH nor GH had a statistically significant effect on hCG binding nor could they mimic the ability of prolactin to allow for LH induction of hCG binding in the hypophysectomized adult male rats. These studies suggest that the induction or “up-regulation” of Leydig cell hCG binding by ovine LH is rapid and specifically dependent upon pre-exposure to prolactin.     

Effect of progesterone on basal LH and episodic LH and FSH secretion in heifers

Heifers between Days 6 and 10 of the cycle were allocated at random to groups of 8 and treated with (i) a 4% progesterone-releasing intravaginal device (PRID) + oestrogen capsule for 12 days; (ii) 4% PRID for 12 days; (iii) 20% PRID for 12 days; (iv) 4% for 14 days; or (v) 20% PRID for 14 days. Blood was obtained daily during treatment and at 2- or 4-h intervals for 72 h after removal of PRIDs. Some animals were sampled every 20 min for 4.676 h on the 3rd day after PRID insertion, and 1 day before and 36 h after removal of the PRID insertion, and 1 day before and 36 h after removal of the PRID. During progesterone treatment there was: (i) no correlation between concentrations of progesterone and LH within days; (ii) a significant negative correlation between progesterone and days (P less than 0.01) and also between progesterone and LH over days (P less than 0.01); (iii) the overall correlation co-efficient between LH and days was positive (P less than 0.05). The amplitude of LH or FSH episodes was not affected as progesterone concentrations declined during PRID treatment, but the number of LH (but not FSH) episodes was increased (p less than 0.01). After PRID removal, the amplitude of both LH and FSH episodes increased (P less than 0.01). We suggest that progesterone is part of a negative feedback complex on LH secretion in cattle and that this effect is apparently mediated through frequency of episodic LH release.     

Diurnal variation in LH and temporal relationships between oscillations in LH and progesterone during the luteal phase in heifers

Diurnal variation in progesterone and LH during the luteal phase and the temporal relationships between oscillations of the two hormones were studied in 10 heifers by collection of blood samples at 0100, 0700, 1300, and 1900 h each day, beginning on Day 1 (Day 0 = ovulation). Concentration of LH on Days 5-9, but not on Days 10-14, was lower (P < 0.05) at 0700 h (0.25 ± 0.02 ng/mL) than at each of the other three hours (combined, 0.32 ± 0.02 ng/mL). An oscillation was defined as an uninterrupted increase and decrease in concentrations. The number of LH oscillations/heifer with the peak at 1900 h (6.1 ± 0.7) throughout the luteal phase was greater (P < 0.01) than for each of the other hours (combined, 4.0 ± 0.2). Diurnal variation in progesterone was not detected. Only statistically defined LH oscillations were used to determine the temporal association between the peak of an LH oscillation and various components of a progesterone oscillation. On Days 5-14, the frequency of the peak of an LH oscillation occurring at the same hour as the peak of a progesterone oscillation (26/48, 54%) was greater (P < 0.0001) than at the progesterone nadir (3/48, 6%). The frequency of the LH peak occurring during increasing (11/34, 32%) and decreasing (8/25, 32%) progesterone concentrations was intermediate (P < 0.05). Results indicated the following: 1) diurnal variation occurred in LH as determined by concentration and by the hour of the peak of an oscillation; and 2) LH oscillations were temporally and positively related to progesterone oscillations.     

Dynamics of excitation energy transfer in the LH1 and LH2 light-harvesting complexes of photosynthetic bacteria.

Photosynthetic light harvesting is a unique life process that occurs with amazing efficiency. Since the discovery of the structure of the bacterial peripheral light-harvesting complex (LH2), this process has been studied using a variety of advanced laser spectroscopic methods. We are now in a position to discuss the physical origins of excitation energy transfer and trapping in the LH2 and LH1 antennae of photosynthetic purple bacteria. We demonstrate that the time evolution of the state created by the light is determined by the combined action of excitonic pigment-pitment interactions, energetic disorder, and coupling to nuclear motion in a pigment-protein complex. A quantitative fit of experimental data using Redfield theory allowed us to determine the pathways and time scales of exciton and vibrational relaxation and analyze separately different contributions to the measured transient absorption dynamics. Furthermore, these dynamics were observed to be strongly dependent on the excitation wavelength. A numerical fit of this dependence turns out to be extremely critical to a variation of the structure and disorder parameters and, therefore, can be used as a test for different antenna models (disordered ring, elliptical deformations, correlated disorder, etc.). The calculated equilibration dynamics in the exciton basis allow a visualization of the exciton motion using a density matrix picture in real space.     

LH release in mink (Mustela vison). Pattern of the LH surge and effect of metabolic status

The mink is a seasonal breeder with induced ovulation and delayed implantation. Reproductive processes are strongly influenced by energy supply and body condition. Items for which there is paucity or complete lack of data were the main objectives of this study: the temporal relationship between copulation and the pre-ovulatory LH surge and the influence of energy supply on LH release. A total of 30 yearling female mink with a well defined metabolic status was used. Twelve females kept in the laboratory were measured in six consecutive one-week balance periods each including the measurement of heat production by means of indirect calorimetry, and 18 females were kept under conventional farm conditions. The animals were fed so as to maintain energy balance (CON), flush fed by 2 weeks food restriction followed by 2 weeks refeeding (FLUSH), or kept in a negative energy balance (NEG). Plasma concentrations of the thyroid hormones, IGF-1 and insulin were determined weekly (n = 12), or 1 week after change in energy supply to the FLUSH group (n = 18). On the day of mating, blood samples for LH and oestradiol-17beta (E2) were taken before and immediately after mating and then 4, 8, 12, 24, 30 and 48 h thereafter. Frequent blood samplings, each lasting 60 min, were taken during the LH surge from two other females surgically fitted with venous access ports. Peak concentrations of LH were recorded on the first sampling, an average 16 min after mating. The concentrations remained elevated for 12 h, but almost decreased to basal values 24 h after mating. Plasma E2 was high before mating and peak values were attained 4 h after mating after which it decreased. Energy supply had no significant influence on LH and E2, but there was a tendency for a more sluggish LH release in NEG animals. The lack of response in FLUSH animals was explained by these animals having a lower intake of metabolisable energy than CON animals, the total intake not being significantly different from the NEG group. Plasma concentrations of thyroid hormones, IGF-1 and insulin were not significantly affected by the treatment, but in FLUSH animals the values mirrored energy supply, and in the NEG group, the values tended to decrease during the course of the experiment. It was concluded that the pre-ovulatory LH surge is an immediate response to mating, and that reproductive activity in the mink is maintained over a wide range of energy supply and body condition.     

Correlation of hypothalamic LHRH, pituitary LH and plasma LH in developing rats.

Hypothalamic LHRH, pituitary LH and plasma LH levels were measured in rats of both sexes from day 5-60 after birth. The content of hypothalamic LHRH was very high in one-week-old male and female rats. It declined gradually till day 17 in the female rat and sharply on day 10 in the male rat. Subsequently the content of hypothalamic LHRH increased and showed peak values on day 25 in the female rat and on day 45 in the male rat. It decreased markedly at respective times of puberty in both sexes (day 37 in the female rat and day 52-60 in the male rat). Results of the study suggest that maturation of hypothalamo-hypophyseal-axis proceeds in three distinct stages. Observations on days 17, 25 and 37 in the female rat and on days 5, 7, 10 and 22 in the male rat clearly show an inverse relationship between hypothalamic LHRH and plasma LH and a parallel relationship between pituitary and plasma LH. Marked decline in the content of hypothalamic LHRH at respective times of puberty in both sexes indicates that the release of threshold levels of LHRH from the hypothalamus may apparently be the event initiating the pubertal changes in rat.     

Impact of single neonatal allylestrenol treatment on the estrus cycle of rats treated with FSH+LH or TSH.

Neonatal allylestrenol treatment administered to female rats significantly increases the duration of estrus phase in the sexual cycle. Treatment with follicle stimulating hormone (FSH) + luteinizing hormone (LH) in adulthood prolongs the duration of estrus even on its own; the effect, however, is more pronounced in those animals who were treated (imprinted) with allylestrenol neonatally. When administered to the control animals, the chemically related thyreotrop hormone (TSH) is either indifferent or it even decreases the estrus index. In animals having received neonatal allylestrenol treatment, however, TSH administration increases significantly the duration of the estrus phase. Either with or without FSH+LH treatment, the ratio of estrogenic to gestagenic phase increases following neonatal allylestrenol treatment. The experiments call attention to the potential functional risks inherent in neonatal allylestrenol treatment. The actual risks, however, seem to be smaller than the effects seen at the receptor level.     

Direct visualization of exciton reequilibration in the LH1 and LH2 complexes of Rhodobacter sphaeroides by multipulse spectroscopy

The dynamics of the excited states of the light-harvesting complexes LH1 and LH2 of Rhodobacter sphaeroides are governed, mainly, by the excitonic nature of these ring-systems. In a pump-dump-probe experiment, the first pulse promotes LH1 or LH2 to its excited state and the second pulse dumps a portion of the excited state. By selective dumping, we can disentangle the dynamics normally hidden in the excited-state manifold. We find that by using this multiple-excitation technique we can visualize a 400-fs reequilibration reflecting relaxation between the two lowest exciton states that cannot be directly explored by conventional pump-probe. An oscillatory feature is observed within the exciton reequilibration, which is attributed to a coherent motion of a vibrational wavepacket with a period of ∼150 fs. Our disordered exciton model allows a quantitative interpretation of the observed reequilibration processes occurring in these antennas.     

The secretion of LH and testosterone in the rabbit.

In the male rabbit, LH and testosterone are secreted as 4–6 discrete pulses per day. The testosterone response to LH is rapid. The testosterone data did not show a normal distribution, but the same data expressed logarithmically were more nearly so. There was no evidence of a 24 h cycle in plasma testosterone levels.