Effect of castration on plasma luteinizing hormone in postpubertal boars

Two experiments were conducted to test the working hypothesis that mean plasma concentrations of luteinizing hormone (LH) increase as a result of an increase in the frequency and amplitude of the pulsatile releases of LH in postpubertal boars after removal of gonadal steroid hormones by castration. It was further hypothesized that these changes in secretion of LH would be the result of changes in sensitivity of the pituitary to gonadotropin releasing hormone (GnRH). In Experiment 1, plasma LH was monitored in 10 postpubertal crossbred boars (13 to 14 mo old and weighing 159 +/- 6.0 kg) at 12-min intervals for 6 h before and 1 h after GnRH (375 ng/kg of body weight) on Days -1, 7, 14, 21 and 29 relative to castration. In Experiment 2, plasma LH was monitored in four castrated and five intact postpubertal boars (11 to 12 mo old and weighing 150 +/- 5.1 kg) after each of three doses of GnRH (94, 188 and 375 ng/kg) were administered to each animal. Sample collection occurred 5 wk after castration. Mean LH and frequency of pulsatile releases of LH increased as a result of castration (P<0.0001), with changes evident by Day 7 after castration. However, the amplitude of the LH pulses increased minimally after castration (P<0.10). The response to exogenous GnRH increased throughout Experiment 1 (P<0.0001), even though the amplitude of the pulsatile releases of LH (response to endogenous GnRH) did not change. Castrated animals in Experiment 2 had a greater response of LH to GnRH stimulation than intact boars (P<0.05). The dose-response curve of castrated animals was not parallel (P<0.001) to that of intact boars, and indicated that sensitivity of the pituitary to GnRH had increased in the absence of gonadal steroids. Thus, the hypotheses stated above can be accepted with the exception that castration may have a minimal effect on LH pulse amplitude. Based on the results of these experiments, we suggest that gonadal steroid hormones modulate both the size of releasable stores of LH and pituitary sensitivity to GnRH in boars.     

Effect of estradiol on secretion of luteinizing hormone during the follicular phase of the bovine estrous cycle

Mean concentrations of luteinizing hormone (LH) increase during the follicular phase of the estrous cycle in cows. The working hypotheses in the present study were (1) that increasing concentrations of 17 beta-estradiol (E2) during the follicular phase of the estrous cycle cause an increase in mean concentration of LH by increasing amplitude of pulses of LH, and (2) that increasing E2 concentrations during this stage of the estrous cycle decrease frequency of pulses of LH in bovine females. Day of estrus was synchronized in seventeen mature cows. Treatments were initiated on Day 16 of the experimental estrous cycle (Day 0 = estrus). At Hour 0 (on Day 16), 4 cows were lutectomized. Lutectomy of these cows (EE; n = 4) allowed for endogenous secretion of E2. The remaining cows were ovariectomized at Hour 0 and were assigned to one of three E2 treatments: luteal phase E2 (LE, n = 5), increasing then decreasing E2 (DE, n = 5), and no E2 (NE, n = 3). Cows in the group that received LE were administered one E2 implant at Hour 0, which provided low circulating concentrations of E2 similar to those observed during the luteal phase of the estrous cycle. Cows in the group that received DE were administered one E2 implant at Hour 0, and additional implants were administered at 8-h intervals through Hour 40; then, two implants were removed at Hours 48 and 56, and one implant was removed at Hour 64.(ABSTRACT TRUNCATED AT 250 WORDS)     

Testosterone, and winning and losing in human competition

Testosterone and cortisol were measured in six university tennis players across six matches during their varsity season. Testosterone rose just before most matches, and players with the highest prematch testosterone had the most positive improvement in mood before their matches. After matches, mean testosterone rose for winners relative to losers, especially for winners with very positive moods after their victories and who evaluated their own performance highly. Winners with rising testosterone had higher testosterone before their next match, in contrast to losers with falling testosterone, who had lower testosterone before their next match. Cortisol was not related to winning or losing, but it was related to seed (top players having low cortisol), and cortisol generally declined as the season progressed. These results are consistent with a biosocial theory of status.     

Influence of dietary-induced weight changes on serum luteinizing hormone, estrogen and progesterone in the bovine female

The working hypothesis in the present study was that changes in concentrations and secretory patterns of luteinizing hormone (LH), 17 beta estradiol (E2), and progesterone in sexually mature beef heifers fed diets deficient in energy are related to changes in body weight of the animals. Another important component of the study was to determine if concentrations and secretion patterns of the reproductive hormones changed over time as feeding of the experimental diets continued. Twelve Red Angus X Hereford heifers (20 mo of age; 355 +/- 7 kg) were assigned randomly to receive a low- (L, n = 7) or high- (H, n = 5) energy diet for 100 days (Day 0 = day of initiation of dietary treatment). All heifers were exhibiting estrous cycles at regular intervals when the experiment was initiated and continued to exhibit estrous cycles at regular intervals throughout the study. Stage of the estrous cycle was synchronized in all 12 heifers by administration of prostaglandin F2 alpha (PGF2 alpha) on two occasions (Days 45 and 75) during the experiment. Serial blood samples (taken at 12-min intervals for 4 h) were collected at 0, 12, 24, 36, 48, and 60 h after the PGF2 alpha injections (Days 45-47 and 75-77) to determine patterns of LH secretion during the follicular phase of the estrous cycle. In addition, serial blood samples (taken at 20-min intervals for 18 h) to monitor LH secretion during the luteal phase of the estrous cycle, in which the stage of the cycle was standardized between heifers, were obtained (Days 59 and 89).(ABSTRACT TRUNCATED AT 250 WORDS)     

Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium

Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel.     

Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal

We have developed a new approach to the measurement of phylogenetic signal in character state matrices called relative apparent synapomorphy analysis (RASA). RASA provides a deterministic, statistical measure of natural cladistic hierarchy (phylogenetic signal) in character state matrices. The method works by determining whether a measure of the rate of increase of cladistic similarity among pairs of taxa as a function of phenetic similarity is greater than a null equiprobable rate of increase. Our investigation of the utility and limitations of RASA using simulated and bacteriophage T7 data sets indicates that the method has numerous advantages over existing measures of signal. A first advantage is computational efficiency. A second advantage is that RASA employs known methods of statistical inference, providing measurable sensitivity and power. The performance of RASA is examined under various conditions of branching evolution as the number of characters, character states per character, and mutations per branch length are varied. RASA appears to provide an unbiased and reliable measure of phylogenetic signal, and the general approach promises to be useful in the development of new techniques that should increase the rigor and reliability of phylogenetic estimates.      

Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis)

Analysis of the heat-shock proteins (hsps) of six closely related species of Poeciliopsis demonstrated the existence of biochemical diversity in the hsp100, hsp70, hsp60, and hsp30 protein families among species. Each species expressed five to seven hsp70-related isoforms. Constitutive 70-kD isoforms were identical among species, but four different patterns of heat-inducible isoforms were seen in these six species. Members of the hsp70 family of molecular chaperones are included among the most highly conserved proteins known, and the possibility of variation in hsp70 among closely related species has rarely been addressed. The hsp30 family is known to be less conserved than the hsp70 family, and, as expected, the Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30 isoforms characteristic of a particular species were unique to that species. Hsp100 and hsp60 were identical in five of the species, but alternate isoforms were found in P. monacha. The small size and limited geographical distribution of the P. monacha population have probably contributed to the uniqueness of the monacha pattern. Two of the species were shown to acquire thermotolerance, the ability to withstand normally lethal temperatures when subjected to a gradual temperature increase. Rapid-heating protocols commonly used to establish critical thermal maxima of organisms do not include this inducible component of thermoresistance and therefore do not adequately assess an organism's capacity to withstand thermal stress.      

Variation in heat shock proteins within tropical and desert species of poeciliid fishes

The 70-kilodalton heat shock protein (hsp70) family of molecular chaperones, which contains both stress-inducible and normally abundant constitutive members, is highly conserved across distantly related taxa. Analysis of this protein family in individuals from an outbred population of tropical topminnows, Poeciliopsis gracilis, showed that while constitutive hsp70 family members showed no variation in protein isoforms, inducibly synthesized hsp70 was polymorphic. Several species of Poeciliopsis adapted to desert environments exhibited lower levels of inducible hsp70 polymorphism than the tropical species, but constitutive forms were identical to those in P. gracilis, as they were in the confamilial species Gambusia affinis. These differences suggest that inducible and constitutive members of this family are under different evolutionary constraints and may indicate differences in their function within the cell. Also, northern desert species of Poeciliopsis synthesize a subset of the inducible hsp70 isoforms seen in tropical species. This distribution supports the theory that ancestral tropical fish migrated northward and colonized desert streams; the subsequent decrease in variation of inducible hsp70 may have been due to genetic drift or a consequence of adaptation to the desert environment. Higher levels of variability were found when the 30- kilodalton heat shock protein (hsp30) family was analyzed within different strains of two desert species of Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In both cases the distribution of hsp30 isoform diversity was similar to that seen previously with allozyme polymorphisms.