Quantitative effect of tenorrhaphy on intrinsic vasculature of the equine superficial digital flexor tendon.

OBJECTIVE: To compare effects of the locking-loop suture pattern (LLP) and 3-loop pulley (3LP) suture pattern for tenorrhaphy on the intrinsic vasculature of the superficial digital flexor tendon (SDFT) of horses in vitro after surgery. SAMPLE POPULATION: 16 forelimbs obtained from 8 mature horses. PROCEDURE: Tenotomy and subsequent tenorrhaphy was performed in anesthetized horses. Following systemic administration of heparin, horses were euthanatized and the limbs were removed and placed under tension to load the flexor tendons. The intrinsic vasculature was then perfused with a mixture of barium sulfate and water. Four-millimeter sections of the SDFT were prepared for microangiographic analysis. Mean vessel density was calculated for each section by use of a grid consisting of 1.5-mm2 vascular assessment squares (VAS). Comparisons were made among the control, LLP and 3LP groups. RESULTS: Mean +/- SD vessel density was 3.11 +/- 0.38, 1.47 +/- 0.47, and 2.01 +/- 0.63 perfused vessels/1.5 mm2 for control, LLP and 3LP groups, respectively. Significant differences in vascular density were detected between the control and 3LP groups, control and LLP groups, and LLP and 3LP groups. CONCLUSIONS AND CLINICAL RELEVANCE: Use of the LLP and 3LP pattern has deleterious effects in vitro on the intrinsic vasculature of the SDFT. However, the 3LP pattern was less disruptive to the intrinsic vasculature, compared with the effects for the LLP. Use of the 3LP tenorrhaphy suture pattern in clinical situations may result in less damage to the intrinsic vasculature of the SDFT of horses during convalescence.

N-methyl D,L-aspartate induces the release of luteinizing hormone-releasing hormone in the prepubertal and pubertal female rhesus monkey as measured by in vivo push-pull perfusion in the stalk-median eminence.

The role of the excitatory amino acid glutamate, N-methyl D-aspartate (NMDA) receptor agonist, in stimulating in vivo luteinizing hormone-releasing hormone (LHRH) release in the stalk-median eminence of conscious prepubertal and pubertal female rhesus monkeys was evaluated using push-pull perfusion. In Exp 1, the effects of i.v. bolus injection of N-methyl D,L-aspartate (NMA) on LHRH release were examined. Injection of NMA induced an increase in LHRH release in all maturational stages of monkeys. Although the LHRH response to NMA tended to be larger in the older groups, only the duration of the LHRH response in the midpubertal group was significantly longer than that in the prepubertal group. In Exp 2, the effects of direct infusion of NMA (0.1, 1, and 100 microM) into the stalk-median eminence on LHRH release were similarly examined. NMA infusion stimulated LHRH release in pubertal monkeys, whereas it did not induce any consistent changes in LHRH release in prepubertal monkeys except for the highest dose. These data suggest that: 1) the systemic injection of NMA is more effective than direct infusion of NMA; and 2) the prepubertal LHRH neurosecretory system is capable of responding to NMDA, although the responsiveness may undergo developmental changes. Therefore, stimulation of NMDA receptors may contribute to the pubertal changes in the LHRH neurosecretory activity.

Progesterone implants enhance SIV vaginal transmission and early virus load.

Simian immunodeficiency virus (SIV) can cross the intact vaginal epithelium to establish a systemic infection in macaques (mac). Using this SIVmac model, we found that subcutaneous progesterone implants, which could mimic hormonally based contraceptives, thinned the vaginal epithelium and enhanced SIV vaginal transmission 7.7-fold over that observed in macaques treated with placebo implants and exposed to SIV in the follicular phase of the menstrual cycle. Progesterone treatment also increased the number of SIV DNA-positive cells in the vaginal lamina propria as detected by in situ polymerase chain reaction analysis. Moreover, plasma viral RNA was elevated for the first three months in macaques with progesterone implants, and three of the progesterone-treated macaques developed relatively rapid disease courses. This study shows that SIV genital infection and disease course are enhanced by subcutaneous implants containing progesterone when compared with the rate of vaginal transmission in the follicular phase.

Ovariectomy increases in vivo luteinizing hormone-releasing hormone release in pubertal, but not prepubertal, female rhesus monkeys.

In pubertal, but not prepubertal, monkeys ovariectomy (OVX) results in an elevation of circulating luteinizing hormone (LH) levels. To determine if the castration-induced LH increase in pubertal monkeys is due to an increase in pulsatile LH-releasing hormone (LHRH) release, effects of OVX on in vivo LHRH release in the stalk-median eminence were examined in fully conscious monkeys using a push-pull perfusion method. The average ages (+/- SEM) of female rhesus monkeys in each group at OVX were 14.5 +/- 0.6 months (n = 6; prepubertal), 25.0 +/- 1.3 months (n = 5; early pubertal) and 37.8 +/- 2.1 months (n = 6; midpubertal). Perfusate samples from the stalk-median eminence were obtained in 10-min fractions for 6 h in the morning (0600 to 1200 h) and 6 h in the evening (1800 to 2400 h), from the same subjects before OVX, and at 29 days and approximately 100 days after OVX. LHRH levels in perfusates were measured by radioimmunoassay. LH levels throughout the experiment were monitored by periodic blood sampling. OVX resulted in a significant LH increase in early and midpubertal monkeys (P < 0.001 for both), but not in prepubertal monkeys. Similarly, OVX in early and midpubertal monkeys increased mean LHRH release when examined 29 days after surgery (P < 0.05 and P < 0.01, respectively). The OVX-induced LHRH increases in early and midpubertal monkeys remained elevated at approximately 100 days postcastration. Furthermore, it was found that effects of OVX on the increased LHRH release were primarily due to the elevation of basal release and pulse amplitude, but not pulse frequency. In contrast, OVX did not cause any significant effects on pulsatile LHRH release in prepubertal monkeys. The results indicate that an increase in LHRH release and a concomitant increase in circulating LH occurs after OVX in pubertal monkeys, but not in prepubertal monkeys. These data are consistent with the hypothesis that the low level of LH in circulation before the onset of puberty is due to a low amount of LHRH release which is independent of ovarian steroid feedback and that the maturity of the neuronal control system for the pulsatile LHRH release is responsible for the onset of puberty. After the onset of puberty, the negative feedback of ovarian steroid hormones becomes important to the regulation of gonadotropin release.

Effect of caffeine on maximal strength and power in élite male athletes.

Computerized testing of 20 élite male athletes was performed to determine the effect of 7 mg kg-1 caffeine on strength and power of the knee extensors and flexors. Subjects received counterbalanced administrations of either caffeine or a placebo on two separate occasions. Peak torque (T) was measured for knee extension (ET) and flexion (FT) at angular velocities of 30 degrees, 150 degrees and 300 degrees s-1. Additionally, performance for the first 125 ms (TAE) and power (W) were recorded during 300 degrees s-1. Testing sessions were held 1 week apart, at which time the placebo/caffeine administration was reversed. A 2 x 2 repeated measures analysis of variance supplemented with a Neuman-Keuls post hoc test showed the following--significant caffeine-related increases (P < 0.05) for ET at 30 degrees s-1, ET at 300 degrees s-1, and ETAE, and EW at 300 degrees s-1. Dependent t-tests performed for pre- to post-test means showed significant changes for the caffeine group in ET at 30 degrees s-1, FT at 30 degrees s-1, FT at 150 degrees s-1, ET at 300 degrees s-1, FT at 300 degrees s-1, E and FTAE, and EW at 300 degrees s-1. No significant effects were found for the placebo trial in any variable. It was concluded that caffeine can favourably affect some strength parameters in highly resistance-trained males. However, differences in subject fibre type, motivation and caffeine sensitivity need to be elucidated.

Effects of electrical stimulation of the medial basal hypothalamus on the in vivo release of luteinizing hormone-releasing hormone in the prepubertal and peripubertal female monkey.

In this study the hypothesis that the LHRH neurosecretory system of the prepubertal female monkey has the capacity to function in a manner comparable to that of monkeys in more mature stages of development was tested. Using push-pull perfusion in the stalk-median eminence, effects of electrical stimulation of the medial basal hypothalamus on in vivo LHRH release were determined in conscious prepubertal, early pubertal, and midpubertal monkeys. After a 180-min period of baseline sample collection, electrical stimulation was applied six times at 90-min intervals via a monopolar electrode, the tip of which was 1-2 mm rostro-dorsal to the perfusion site. Control experiments were performed in the same manner, but without electrical stimulation. During control perfusions, the mean LHRH level remained stable. Mean (+/- SEM) LHRH release for the entire perfusion period in control experiments was 0.5 +/- 0.2, 2.4 +/- 0.4, and 2.2 +/- 0.7 pg/ml.10 min for the prepubertal (n = 6), early pubertal (n = 4), and midpubertal (n = 6) groups, respectively. Mean LHRH release in the prepubertal group was significantly lower than that in either of the older groups (P less than 0.05). In contrast, in all three age groups, repeated electrical stimulation of the medial basal hypothalamus resulted in 1) a short latency increase in LHRH release occurring within 20 min after each stimulation, and/or 2) a gradual increase in mean LHRH release over several hours. In the prepubertal group (n = 4), mean LHRH levels were 0.8 +/- 0.5 pg/ml.10 min during the 90 min before the first electrical stimulation and increased to 6.1 +/- 2.9 pg/ml.10 min during the 90 min after the sixth stimulation. This degree of responsiveness was similar to that of the older age groups. Mean LHRH levels before stimulation were 1.3 +/- 0.6 and 2.4 +/- 1.1 pg/ml.10 min in the early pubertal (n = 5) and midpubertal (n = 5) groups, respectively, and increased to 7.8 +/- 3.5 and 6.0 +/- 1.8 pg/ml.10 min, respectively, after the sixth stimulation. These increases in LHRH concentration with electrical stimulation were significant for all three age groups (P less than 0.03-0.001), while there were no significant differences between age groups. The temporal patterns of these responses suggest that electrical stimulation elicits LHRH release with a similar magnitude in all three age groups by 1) depolarizing LHRH neurons directly, and/or 2) stimulating multineuronal systems that synapse with LHRH neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Sexual differentiation of the mechanism controlling pulsatile secretion of luteinizing hormone contributes to sexual differences in the timing of puberty in sheep.

Sexual differences in the regulation of tonic luteinizing hormone (LH) secretion were examined in immature female and male sheep (eight each, including six pairs of female/male twins). After gonadectomy of lambs at 2 weeks of age, Silastic capsules filled with estradiol, a primary central feedback steroid in both females and males, were implanted every 3 weeks for 3 days, and then removed, so that the pattern of LH secretion could be repeatedly determined in the same individuals both with and without steroid feedback. Implanted capsules yielded circulating steroid levels of 2-5 pg/ml. Circulating LH concentrations were determined by radioimmunoassay in blood samples collected at 12-min intervals for 4 h immediately before estradiol was implanted, and again, immediately before it was removed 3 days later. In male lambs, a decrease in responsiveness of the hypothalamic-pituitary axis to inhibition by estradiol began at 8-11 weeks, as evidenced by the progressive increase in mean LH concentrations and frequency of LH pulses. This correlated temporally with the onset of spermatogenesis in intact male controls (n = 8). In females, a similar decrease in responsiveness did not occur until 26-29 weeks of age, corresponding to the onset of ovulatory cycles in intact female controls (n = 6). In the absence of estradiol implants, LH pulse frequencies were higher in male lambs than in female lambs between 5 and 35 weeks of age. There was no further increase in LH pulse frequency in the absence of the gonads in either sex during the pubertal period. These findings suggest that the mechanism regulating tonic LH secretion in developing lambs is sexually differentiated in its responsiveness to inhibition by estradiol. This differentiation also occurs at a more fundamental steroid-independent level, but any causal relationship between the higher steroid-independent LH pulse frequency and the lower responsiveness to estradiol negative feedback in males is not evident. We hypothesize that these sexual differences in the regulation of tonic LH underlie the difference in the timing of puberty in male and female lambs.

The ontogeny of melatonin secretion in the lamb.

In the female lamb, early postnatal photoperiod treatments do not alter the timing of puberty as do treatments at later ages. In the male lamb, early photoperiod treatments also fail to influence reproductive development. This prompted the hypothesis that the very young lamb may be unable to transduce changes in daylength into appropriate endocrine cues for puberty. The hypothesis was evaluated by determining the ontogeny of pineal melatonin secretory patterns in both female (n = 4-6) and male (n = 4) lambs under natural photoperiods. Serum melatonin concentrations were determined by a modified RIA in samples collected hourly for 24 or 48 h. Clustering analysis was used to define elevated and nonelevated periods of melatonin secretion. Elevated secretion was evident at night in six of eight lambs by 1 week of age and in all lambs by 3 weeks of age. In nearly all cases, the elevated nighttime levels accurately and consistently reflected the duration of the dark period. The mean amplitude of the elevated nighttime melatonin secretion was low in very young lambs and increased with age. No difference between females and males was observed in either the amplitude or duration of the nocturnal melatonin rise. Our results do not support the hypothesis that the failure of early photoperiod treatments to influence reproductive development is due to an inability of the young lamb to transduce photoperiod patterns into an endocrine signal. Rather, they suggest that some other aspect of reproductive neuroendocrine function is restrictive at these ages.

Amplitude modulation of the nightly melatonin rise in the neonatal lamb and the subsequent timing of puberty.

Spring-born female lambs require a decrease in day length for the normal timing of puberty the following autumn. If this decrease occurs early in postnatal life (i.e. 0-10 weeks), puberty is delayed. This study tested the hypothesis that failure of the neonatal lamb to respond to the critical long-day to short-day signal is due to inadequate nocturnal melatonin secretion. The approach was to artificially increase, to adult levels, the low nighttime rises of melatonin during the early postnatal period. Eight female lambs served as controls; they were raised on short days until 17 wk of age, and then exposed to 5 wk of long days, after which they were returned to short days. This alternating sequence of photoperiods during mid-development would be expected to induce normal puberty. Sixteen experimental females were exposed to the critical block of long days much earlier; they were placed in long days between 2 and 7 wk of age and in short days thereafter. Half (n = 8) received no further treatment. The other half (n = 8) were infused nightly with melatonin during the 8-h dark phase of the 5-wk, long-day photoperiod. This increased the amplitude of the natural nighttime melatonin rises 3- to 4-fold, well into the adult range.(ABSTRACT TRUNCATED AT 250 WORDS)

Entrainment of the melatonin rhythms in early postnatal lambs and their mothers.

Although the developing sheep can produce an appropriately timed melatonin rhythm as early as 1 week after birth, it is not known whether the lamb is able to adjust its melatonin rhythm to a change in daylength. The ability of the young lamb to entrain its pattern of melatonin secretion to a new photoperiod was determined in the present study. Eight female lambs and their mothers were raised in long days (LD 16:8) beginning 2 weeks postpartum. At 7 weeks of age, the time of lights-off was advanced 8 hr, the short-day photoperiod then being LD 8:16; the time of lights-on remained unchanged. Concentrations of melatonin were measured in blood samples collected hourly on days - 1, 0, 2, 4, 6, and 13 relative to the light change. On day 0, all mothers and daughters had advanced the onset of melatonin secretion by at least 1 hr, and by day 13, 12 of 16 had completely entrained to the new photoperiod. The rate of entrainment among individuals varied; the mean rate for lambs and mothers did not differ. This study provides evidence that the melatonin-rhythm-generating system matures shortly after birth.

Neuroendocrine responsiveness to light during the neonatal period in the sheep.

Circulating prolactin concentrations were monitored during the early postnatal period in sheep to evaluate their response to photoperiod. In the first experiment, male and female lambs were exposed from 1 week of age, with their mothers, to either long days (16 h light: 8 h darkness; n = 15) or short days (8 h light: 16 h darkness; n = 16) to test whether they could discriminate different day lengths. In both sexes, serum prolactin concentrations were higher on long than on short days during the first 7 weeks after birth. In the second experiment, female lambs (n = 21) were raised on long days from 2 weeks of age. The superior cervical ganglia were removed bilaterally at 4 weeks of age from 14 lambs to lesion the sympathetic innervation to the pineal gland, and thus ablate the nocturnal increase in pineal melatonin secretion. After surgery, serum prolactin concentrations on long days were significantly lower in ganglionectomized lambs than in the intact controls. In the third experiment, the amplitude of the night-time melatonin rise was artificially increased in female lambs (n = 8) between 2 and 7 weeks of age to adult levels. Unrestrained lambs were infused during the 8-h dark phase of each day with melatonin by means of a self-contained, computerized syringe-pump. Concentrations of circulating prolactin did not differ from those in uninfused lambs (n = 8) with lower endogenous nocturnal melatonin. These results reveal that the sheep can discriminate photoperiod cues during the early postnatal period, and suggest that the low-amplitude melatonin rhythm in the neonatal lamb is sufficient to mediate this response.

Cessation of long day melatonin rhythms time puberty in a short day breeder.

This study tested the hypothesis that in the female sheep, a short day (SD) breeder, puberty can occur normally in the absence of ambient short days. More specifically, the photoperiod cue timing the transition into adulthood is exposure to and then termination of a long day melatonin rhythm. Control lambs born in the spring were exposed to 5 weeks of long days (LD; 16 h of light, 8 h of darkness; 18-23 weeks of age) and were raised in SD (8 h of light, 16 h of darkness) at other times. As expected from previous studies, this alternating photoperiod sequence (SD-LD-SD) induced puberty at the normal age in autumn [33 +/- 2 weeks (mean +/- SEM); n = 6]. The other three groups were exposed only to LD from birth; the superior cervical ganglia were removed bilaterally at different ages to denervate the pineal gland in order to block transduction of subsequent LD cues. Puberty occurred normally (31 +/- 1 weeks; n = 7) after ganglionectomy at 23 weeks of age, indicating that ambient short days are not required to initiate reproductive cycles. LD are necessary, as evidenced by the results for the other two groups ganglionectomized neonatally at 4 weeks of age. With no further treatment, puberty was either delayed (n = 1) or did not occur during the first year of life (n = 5), after which the study ended. This delay was prevented in the other group of ganglionectomized lambs by a 5-week (18-23 weeks of age) exposure to LD melatonin patterns by means of 8-h melatonin infusions nightly; 12 weeks after melatonin replacement therapy, puberty occurred at the normal time (34 +/- 1 weeks; n = 6). The inference is that for puberty to occur in the female lamb the animal must be exposed to relatively limited periods of LD, followed by the blockade or absence of further LD cues (pineal denervation, termination of LD melatonin infusion, or presence of SD). This supports the concept that the LD of summer, followed by their disappearance in autumn, time puberty in the female sheep.

Are ambient short-day cues necessary for puberty in a short-day breeder?

Some exposure to long days (LD) is necessary for female sheep to achieve puberty during short days (SD). In this regard, a 5-wk block of long days in lambs otherwise raised in short days will result in puberty at the normal age. In the present study, Suffolk lambs were raised in various artificial photoperiods to assess the role of short days. An increase in circulating progesterone to luteal phase levels was used as the criterion for puberty. Controls exposed to short days except for 5 wk of long days between 17 and 22 wk (SD-LD-SD) began repetitive reproductive cycles at the expected age (34 +/- 0.7 wk, mean +/- SE). When the final block of short days was eliminated and exposure to long days was continued after 22 wk of age (SD-LD-LD), puberty was delayed (41 +/- 0.8 wk of age). Removal of the first block of short days (LD-LD-SD) did not prevent normal puberty, and the initiation of cycles (29 +/- 0.9 wk) occurred earlier than in controls. Lambs in which the pineal gland was denervated at 22 wk so that it was unable to transduce short-day cues after exposure to long days (SD-LD-X) exhibited puberty at an age (33 +/- 1.2 wk) similar to that of controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Timing of puberty by photoperiod.

Photoperiod cues play an important role in the timing of puberty in the female lamb. Removal and replacement of photoperiod cues by denervation of the pineal gland and timed melatonin infusions, respectively, indicate that the pathway for transmission of photoperiod information develops well before puberty. This is reinforced by manipulation of artificial photoperiods during various periods of development. Such approaches reveal that even in the first few weeks of life, the pattern of melatonin secretion accords with daylength and modulates prolactin secretion. Several months later, after internal, growth-related cues indicate that sufficient body size has been achieved to initiate reproduction, photoperiod history is used as an important predictor of reproductive success, and thus, whether puberty should occur. In the female spring-born lamb, the decrease in daylength in autumn is the critical cue for the initiation of estrous cycles. Experimentally, this may be achieved by surgically disrupting the pathway for transmission of photic cues after appropriate long-day exposure. In the autumn-born lamb and in the slowly growing lamb, sexual maturation may be masked by the transition into seasonal anestrus the following spring. In these young females, a decreasing photoperiod or "removal of long days" (surgical) is not necessary for puberty the following autumn. Sufficient photoperiod history may be acquired in such lambs that they enter puberty as a consequence of becoming refractory to the long days of summer. We hypothesize that the phenomenon of refractoriness reflects the expression of an innate rhythm of reproductive activity and that changes in daylength experienced early in life serve to synchronize this rhythm with the seasonal environment.

Determination of a fatigue curve as a function of electromyography and mechanical work.

The purpose of this study was to identify a fatigue curve in which muscle electrical activity was a function of the mechanical work performed by the anterior tibialis muscle. A work fatigue curve was determined to be the function of a cubic regression equation. The work fatigue curve was compatible with the accepted physiological concept of at least two different muscle fiber types.J Orthop Sports Phys Ther 1984;5(6):332-335.