Search PubMed⌕ Search

Biomedical subjects

R D MacDonald

Publications and source records attributed to R D MacDonald.

10 recordsLinked to original sources
PubMed1997

Acute dapsone intoxication: a pediatric case report.

INTRODUCTION: There are many case reports of dapsone overdose in adults but only a few reports of dapsone-induced methemoglobinemia in children. We report a case of a three-year-old boy who developed prolonged recurrent methemoglobinemia following an ingestion of dapsone. METHODS: Case report. ETHICS: Not applicable. STATISTICS: Not applicable. RESULTS: This child developed significant symptoms of methemoglobinemia approximately two hours after ingesting dapsone 37.5 mg/kg. The initial methemoglobin level measured 2.5 hours after ingestion was 44%. The patient was treated with multiple doses of activated charcoal and methylene blue. Three doses of methylene blue reduced the methemoglobin level to 6% by approximately 16 hours after the overdose but the level rebounded to nearly 15% at 64 hours postingestion. DISCUSSION: Dapsone is a drug that is being used for a wide variety of clinical conditions. The primary clinical manifestation of dapsone overdose is methemoglobinemia. An important aspect of dapsone poisoning is its ability to produce methemoglobinemia, which is long lasting and which may recur following methylene blue therapy. Because of this, dapsone-poisoned children need to be monitored for two to three days.

Antimalarials↗
PubMed1993

Age-related changes in the secretion of growth hormone in vivo and in vitro in infantile and prepubertal Holstein bull calves.

The average concentration of GH in blood is high at birth and declines during the period of sexual maturation in bulls. The objectives of these studies were (1) to define age-related changes in vivo in the pulsatile secretion of GH from birth to puberty, (2) to determine whether pituitary cell content of GH and characteristics of the secretion of GH in vitro reflect age-related changes in vivo, and (3) to examine whether responsiveness to GH-releasing hormone (GHRH) and somatostatin (SRIF) in vitro changed with age in Holstein bull calves. In experiment 1, calves were bled every 15 min for 12 h at < 1, 12 and 42 weeks of age (n = 5/group), these being representative of infantile, juvenile and pubertal stages of development. Calves were killed 3 to 5 days later and the pars distalis of the anterior pituitary gland was enzymatically dispersed into a suspension of single cells. Aliquots of cells were extracted with 0.01 mol NaHCO3/l to determine the content of GH and cultured for 18 and 72 h. As expected, the average concentration of GH in plasma decreased with age (P < 0.001). The initial decrease in GH was caused by a reduction in the baseline concentration between birth and 12 weeks of age. There was a marked decrease in GH pulse amplitude between 12 and 42 weeks of age and a further reduction in the baseline concentration. In contrast, the pulse frequency of GH increased (P < 0.05) from < 1 week to 12-weeks of age and remained constant thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1993

Testicular development in bulls treated with recombinant bovine somatotropin.

This study was conducted to test the hypothesis that administering recombinant bovine somatotropin (rbST) would affect testicular development in Holstein bulls. From 4 until 32 wk of age, bulls received a daily injection of either placebo (C) or rbST (.2 mg/kg BW.75, i.m.; n = 10/group). At 14-d intervals, blood was obtained and assayed for testosterone (T); BW, shoulder height (SH), and testis length (TL) were recorded. At 7, 12, and 24 wk of age, bulls were bled at 10-min intervals for 6 h to determine the secretory patterns of LH, growth hormone (GH), and IGF-I. All bulls were killed at 40 wk of age. One testis was used for determination of daily sperm production (DSP), and the number of spermatids per gram of parenchyma (SP/G); the remaining testis was perfused and fixed for histological analysis of numbers of Sertoli cell nuclei (SCN/ST) and spermatids per seminiferous tubule cross-section (SP/ST). Epididymal spermatozoa were collected to test effects of rbST on the integrity of spermatozoal chromatin structure. Administration of rbST increased (P < .0001) concentrations of GH (nanograms/milliliter) in plasma at all ages (C vs rbST; wk 7, 8.9 +/- 1.0 vs 51.9 +/- 6.8; wk 12, 12.8 +/- 1.4 vs 59.2 +/- 6.4; and wk 24, 5.2 +/- 1.5 vs 42.6 +/- 12.2). There was an age x treatment interaction (P < .0183) for concentrations of IGF-I (nanograms/milliliter) in plasma (C vs rbST; wk 7, 149.7 +/- 6.1 vs 148.6 +/- 8.6; wk 12, 184.1 +/- 12.8 vs 216.6 +/- 15.9; and wk 24, 392.8 +/- 24.8 vs 484.7 +/- 19.9).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Prepubertal changes in plasma FSH and inhibin in Holstein bull calves: responses to castration and(or) estradiol.

The objectives of two studies were to determine 1) whether plasma concentrations of inhibin (INH) changed with age in prepubertal bulls and whether these changes were related to changes in FSH, testosterone or testis length; and 2) whether castration and(or) estradiol implants affected plasma concentrations of INH and FSH. In Exp. 1, plasma INH remained constant from 4 until 8 wk of age then increased from 120 pM to 202 pM between 8 and 12 wk. Thereafter, INH decreased to 90 pM by 36 wk. Between 4 and 10 wk, plasma FSH increased from .32 to .43 ng/ml, apparently increasing before the initial rise in plasma INH. Between 10 and 12 wk, FSH declined from .43 to .33 ng/ml. After 12 wk, FSH increased as INH decreased. Initial increases in testis length and concentrations of plasma testosterone occurred at 14 wk coincident with the second rise in FSH. In Exp. 2, bull calves were either left intact, castrated, castrated and implanted with estradiol, or left intact and implanted with estradiol at 7.5 wk of age. Castration decreased concentrations of INH and increased concentrations of FSH. Castrated calves implanted with estradiol had decreased concentrations of both INH and FSH. Intact bulls implanted with estradiol had decreased concentrations of FSH relative to intact unimplanted bulls; however, concentrations of INH did not display the age-related changes observed in intact, unimplanted bulls. In summary, age-related changes in plasma INH and FSH occur in bulls. Furthermore, plasma concentrations of INH and FSH increased before changes in gonadal size were detected. The bovine testis may be a major source of circulating INH because castration decreased concentrations of plasma INH.

Aging↗
PubMed1990

Effect of naloxone on the secretion of LH in infantile and prepubertal Holstein bull calves.

Administration of naloxone (100 mg i.v.; approximately 1.21 mg/kg body weight0.75) to 10 intact calves (24 weeks of age) caused an acute release of LH that was similar in amplitude and duration to spontaneous discharges of LH that occur at the same age. The naloxone-induced release of LH was abolished in 9/10 calves (intact and castrated) treated with oestradiol-17 beta. To determine the ontogeny of opioid control of secretion of LH, 12 calves were randomly assigned to receive saline or naloxone (1.21 mg/kg body weight0.75, i.v.) at 3, 5, 7, 9, 11, 13, 17 and 21 weeks of age. At each age, blood was collected at 10-min intervals for 4 h and saline or naloxone was administered (i.v.) after collection of the 120-min sample. Before administration of naloxone, plasma LH values increased with age (P less than 0.01) but did not differ between the control and naloxone groups (age x treatment, P greater than 0.05). Administration of naloxone caused concentrations of plasma LH to increase at 3, 11, 13, 17 and 21 weeks of age (treatment x time, P less than 0.001). Concentrations of LH (saline vs naloxone, ng/ml) reached a maximum within 20 min after treatment at Weeks 3 (0.3 vs 1.2), 11 (0.6 vs 2.6), 13 (0.6 vs 3.7), 17 (1.1 vs 2.6), and within 40 min after treatment at Week 21 (1.0 vs 3.5).(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1986

Luteinizing hormone response to pulsatile luteinizing hormone-releasing hormone in prepubertal heifers.

The effects of 12 hourly 5-micrograms injections of luteinizing hormone-releasing hormone on luteinizing hormone release, were examined in 18 prepubertal Holstein heifers at 4, 7, or 10 mo of age. During a 6-h pretreatment period, mean serum luteinizing hormone concentrations and mean number of endogenous luteinizing hormone episodes per hour were not influenced by age. The 12-h treatment regimen induced a pulsatile release of luteinizing hormone in all heifers. The magnitude, pattern, and total amount of luteinizing hormone released were not influenced by age. However, in the 4 and 10-mo-old age groups, magnitude of luteinizing hormone response to the 3rd hourly injection of luteinizing hormone-releasing hormone was greater than the response to the second injection. Magnitudes of luteinizing hormone responses decreased with time after the 4th hourly injection through the 12th injection and patterns of decline appeared similar among the three age groups. The pituitary of the prepubertal dairy heifer is able to respond to an hourly pulsatile administration of luteinizing hormone-releasing hormone and this treatment regimen appears to produce a self-priming effect on luteinizing hormone release.

Animals↗