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Biomedical subjects

K D Ryan

Publications and source records attributed to K D Ryan.

11 recordsLinked to original sources
PubMed1991

Myelodysplasia--the musculoskeletal problem: habilitation from infancy to adulthood.

The physical therapy and orthopedic management of patients with myelodysplasia from infancy to adulthood are reviewed. The overall goal for the child with myelodysplasia is functional independence. Physical therapy and orthopedic intervention enable the individual to achieve this goal. Associated problems, however, such as Arnold-Chiari malformation, hydrocephalus, and tethered spinal cord, influence functional expectations. Physical therapy management begins in the neonatal period and continues through adolescence. Treatment is modified at the various stages of development. Knowledge of current orthotic and adaptive equipment is necessary to achieve optimal locomotor function. Orthopedic management decisions are based on musculoskeletal and neurologic assessments, to which the physical therapist provides a significant contribution. Controversies exist over the orthopedic management of dislocated hips, scoliosis, and kyphosis.

Adolescent↗
PubMed1991

Patterns of circulating gonadotropins and ovarian steroids during the first periovulatory period in the developing sheep.

This report provides evidence that an increment in serum gonadotropin levels occurs at puberty in the sheep and that this reflects the critical hormonal event culminating in first ovulation in this species. Blood samples were collected from 6 female lambs at 4-h intervals for a period of approximately 2 mo around the expected time of puberty (32 wk of age) until behavioral estrus was observed and ovulation was verified by assay of serum progesterone. Patterns of circulating LH, FSH, progesterone, and estradiol concentrations were characterized during the peripubertal period for each lamb. A rise in serum levels of both LH and FSH began approximately 7-10 days before the first preovulatory surge of gonadotropins. Although the increase in gonadotropin levels occurred gradually over several days, serum estradiol levels rose only during the final 40-60 h prior to the preovulatory surge of gonadotropin. Serum progesterone profiles revealed, however, that normal (14-16-day) luteal phases were induced in only 2 of 6 females as a result of the first surge. In four lambs, a short luteal phase of 2.5 days' duration occurred, which was followed by another estradiol rise and a preovulatory surge that then resulted in a full luteal phase of 14 days' duration. These data demonstrate clearly that the precipitating event at puberty in the female sheep is an increase in circulating gonadotropin levels and that the estradiol secreted from the newly stimulated follicle provides the signal for the first preovulatory surge.

Animals↗
PubMed1989

Prolactin or dopamine mediates the induction of puberty by long days in female ferrets.

The role of PRL in sexual maturation of female ferrets was examined in these studies. Longitudinal profiles of PRL secretion were obtained by thrice weekly blood sampling of intact female ferrets undergoing photoperiod-stimulated development as well as age-matched control females which remained in nonstimulatory short days. Two additional groups of intact females, one in each photocycle, were treated with the dopamine agonist drug bromocriptine throughout the study. The relationship between developmental changes in PRL secretion and the critical pubertal decrease in the efficacy of estradiol (E2) inhibitory feedback on LH secretion was studied by using additional groups of females which were ovariectomized and treated with E2 implants (OVX + E2). These latter females were housed in either long or short day photoperiods; some were treated with bromocriptine, the remainder were treated with the vehicle only. Results of this study revealed that PRL secretion in ferrets does not change acutely with an abrupt increase in day length. After 4 weeks of exposure to long days, however, a marked increase in PRL secretion occurred. This increased secretion of PRL was contemporaneous with the onset of pubertal ovarian activity in intact females and with the escape of LH from the negative feedback of E2 in OVX + E2-treated females. The further observation that pharmacological blockade of the long day-induced rise in PRL secretion also prevented the pubertal onset of ovarian activity suggested that PRL may play a critical role in the induction of puberty in this species. The mechanism by which bromocriptine prevented puberty induction was illustrated in the OVX + E2-treated ferrets in stimulatory photoperiod. The drug treatment prevented the pubertal decrease in the efficacy of E2 negative feedback on LH. These studies suggest an important interaction between the dopamine-PRL system and the GnRH-LH system in the regulation of sexual maturation of female ferrets.

Animals↗
PubMed1988

Sexual maturation in the female ferret: circumventing the gonadostat.

The purpose of this study was to examine the role of circulating 17 beta-estradiol in the regulation of pituitary gonadotropin secretion and, hence, ovarian maturation in immature female ferrets. The hypersensitive negative feedback relationship between the ovaries and the hypothalamo-pituitary axis in developing ferrets was disrupted by infusion of a specific antiserum to 17 beta-estradiol. The effect of this treatment on gonadotropin secretion and ovarian morphology was contrasted with that observed in intact age-matched control females treated with a nonimmune gamma-globulin preparation. Infusion of the antibody into intact immature ferrets caused, within 48 h, an increase in pulsatile secretion of LH to 0.67 +/- 0.06 pulses/h over that observed in intact females treated with control gamma-globulin (0.13 +/- 0.06 pulses/h). This increase in pulse frequency was similar to that observed 48 h after ovariectomy of young animals (0.70 +/- 0.12 pulses/h). Furthermore, this level of gonadotropin secretion in antibody-treated animals resulted in stimulation of antral follicle growth in ovaries of these females. Ferrets treated with specific antiserum to 17 beta-estradiol showed a significant increase in numbers of ovarian follicles greater than 0.3 mm in diameter compared to those in ovaries of females treated with control gamma-globulin. These data strongly suggest that the limiting event at puberty in the ferret is the rise in gonadotropin secretion which is allowed by the pubertal decrease in efficacy of 17 beta-estradiol to inhibit gonadotropin secretion.

Animals↗
PubMed1987

A study of spontaneous sexual maturation of the female ferret.

Although ferrets are long-day breeders, females reared exclusively in nonstimulatory short days will undergo spontaneous sexual maturation by 30-50 wk of age. In the following report, this spontaneous sexual maturation of ferrets was studied to determine mechanisms regulating sexual maturation in nonstimulatory photoperiods. Study of ovariectomized females treated with low, constant levels of estradiol suggest that a marked decrease in the efficacy of estradiol to inhibit luteinizing hormone secretion occurs shortly before sexual maturity becomes evident in intact controls (both groups housed in short days). During this long juvenile period, a marked increase in body weight occurred, but ovarian responsiveness to exogenous gonadotropin did not change. Older, larger females did respond more rapidly to stimulatory photoperiod than did younger females. These studies suggest that the mechanisms of spontaneous puberty in ferrets are likely the same as those regulating photoperiod-stimulated puberty in this species.

Animals↗
PubMed1978

Ontogeny of pulsatile luteinizing hormone and testosterone secretion in male lambs.

The ontogeny of pulsatile LH and testosterone (T) secretion was studied in the developing male sheep. Three variables of LH secretion (frequency of LH pulses, magnitude of LH pulses, and the levels between pulses) were determined during a 6-h period at each of 1, 2, 3, 5, 7, 8, 12, and 16 weeks of age in six male lambs. Pulsatile LH secretion was evident by 1-2 weeks of age in rapidly growing lambs and by 3-7 weeks of age in slowly growing lambs. Although mean height of LH discharges increased 2-fold after the onset of pulsatile release, levels between discharges remained constant throughout the entire study. The most striking change, however, occurred in the frequency of LH discharges. The frequency increased 20-fold between weeks 1 and 8 and then decreased 3-fold between weeks 8 and 16. In each lamb, a brief (less than 3 h), but marked rise (greater than 2 ng/ml) in levels of circulating T occurred after the first observed pulse of LH. Thereafter, as the lambs became older, increased concentrations of serum T were observed only during periods of pulsatile LH secretion, the highest mean level of T occurring about 1 h after each LH peak. Administration of human chorionic gonadotropin (hCG) iv to 2-day-old males resulted in a marked increase in circulating T. A greater increment in concentrations of serum T occurred after the same absolute dose (50 IU) of hCG at 8 weeks of age than at 2 days of age. These results indicate that in the male lamb 1) pulsatile secretion of LH is initiated shortly after birth and changes in mean levels of LH are primarily a reflection of changes in frequency of LH discharges; 2) before the onset of pulsatile LH secretion, the testes are capable of responding to an exogenous LH-like gonadotropin with increased secretion of T; 3) after the onset of pulsatile LH secretion, a rise in circulating T follows each pulse of LH; and 4) an increase in capacity of the testes to secret T occurs during the first 8 weeks of postnatal life. It is concluded that the pattern of LH secretion, coupled with the capacity of the testes to secrete T, determines the pattern and magnitude of T secretion in the developing male sheep.

Animals↗