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Biomedical subjects

J B Hall

Publications and source records attributed to J B Hall.

At least 19 recordsLinked to original sources
PubMed1996

The controversy over emergency research. A review of the issues and suggestions for a resolution.

Emergency research that occurs upon critically ill subjects in circumstances that do not allow the subjects or their legally authorized representatives to grant an informed consent is currently the subject of great controversy. This Clinical Commentary reviews three issues that dominate the debate: research risk assessment, the concept of a particular kind of risk called minimal risk, and the regulations governing research on human subjects. The theses of this article are that Institutional Review Boards (IRBs) are not violating Office of Protection from Research Risks (OPRR) regulations, that Food and Drug Administration (FDA) regulations do not adequately address research design, and that emergency research fits within the ethical standards of justice, respect for autonomy, and beneficence. To defend these claims, the following points are argued: risk assessment is a moral or transscientific exercise, minimal risk refers to the increment of risk that the subject of the research faces, and that when equipoise exists between experimental and standard therapies, this state of uncertainty contributes to a study's justifications. In order to resolve the emergency research controversy, certain regulations will need to be rewritten and others reinterpreted, and a national board created to review a proposed study's clinical relevance and whether the current state of knowledge justifies a trial.

Critical Illness↗
PubMed1996

Sedation of critically ill patients during mechanical ventilation. A comparison of propofol and midazolam.

Propofol (P) and midazolam (M) are frequently given by continuous infusion for sedation in critically ill, mechanically ventilated patients. We compared these drugs with regard to: (1) time-to-awaken; (2) reproducibility of bedside assessments of level of sedation; (3) time-to-sedation; and (4) change in oxygen consumption (V O2) from awake to sedated state. Seventy-three patients were prospectively randomized to receive either P (n=37) or M (n=36). Wake-up times after stopping the drug were assessed by blinded and unblinded observers, by asking patients to perform simple tasks. Times to sedate were assessed by consensus agreement among nurses and investigators. Demographics and APACHE II scores were not different between P and M. The P group had a significantly narrower range of wake-up times with a higher likelihood of waking in less than 60 min. Blinded versus unblinded observations had excellent correlation. Average time to sedate and decrease in V O2 were not different. We conclude that in this patient population: (1) both P and M achieved optimal sedation in a large fraction of patients when administered by specified dosing protocols; (2) P had a faster, more reliable, wake-up time; (3) assessments of time-to-awaken were objective and reproducible; (4) time to sedation was not significantly different; (5) V O2 decreased similarly with both.

APACHE↗
PubMed1996

Life-threatening effects of discontinuing inhaled nitric oxide in severe respiratory failure.

We present the effects of abrupt discontinuation of inhaled nitric oxide (NO) in four patients with severe hypoxemic respiratory failure. These patients ranged from 9 mo to 65 yr of age. In each patient, after the initiation of inhaled NO, a marginal, but immediate, beneficial effect on gas exchange and, when measured, a reduction in pulmonary artery pressures was noted. However, during attempts to discontinue inhaled NO, not only did these patients develop worsening oxygenation and recrudescence of pulmonary hypertension but, unexpectedly, these parameters were worse than the baseline values, leading to life-threatening hemodynamic instability. These effects reversed immediately after reinstitution of inhaled NO. The mechanism of this severe ¿rebound¿ in pulmonary hypertension after abrupt withdrawal of NO is unclear, but its existence emphasizes the need to avoid a substantial risk to these patients. Moreover, we believe that both unintentional and intentional termination of inhaled NO therapy may lead to life-threatening deterioration in gas exchange and circulatory hemodynamics that exceeds the initial therapeutic benefit.

Administration, Inhalation↗
PubMed1995

Intraperitoneal foreign body as a cause of acute abdomen in pregnancy.

Although surgical textbooks commonly include foreign bodies in the differential diagnosis of acute abdomen, this cause of abdominal pain has not been reported in the obstetric literature. A 35-year-old woman presented at 24 weeks' gestation with right lower quadrant pain and peritoneal signs. The only abnormal finding at exploratory laparotomy was a free-floating intraperitoneal foreign body, presumably left inadvertently during prior surgery. The differential diagnosis of acute abdomen in pregnancy should include intraperitoneal foreign body in any woman with a history of previous abdominal surgery.

Abdomen, Acute↗
PubMed1995

Pulmonary artery diastolic-occlusion pressure gradient is increased in acute pulmonary embolism.

OBJECTIVE: To assess the pulmonary artery (PA) diastolic-occlusion (wedge) pressure gradient in patients with acute pulmonary embolism and to evaluate this variable's diagnostic utility. DESIGN: Retrospective, clinical review. SETTING: Intensive care and cardiac catheterization units of a university medical center. INTERVENTIONS: None. PATIENTS: A series of 19 acute pulmonary embolism patients with concurrent right heart catheterization. Control groups consisted of 19 age-, sex-, and heart rate-matched critically ill controls who also underwent right heart catheterization, eight patients suspected of having pulmonary embolism who had negative pulmonary angiography and concurrent right heart catheterization, and 255 patients with a primary diagnosis of coronary artery disease who underwent right heart catheterization at the time of left heart catheterization. MEASUREMENTS AND MAIN RESULTS: Initial hemodynamics (systolic, diastolic, and mean systemic and pulmonary arterial pressures, occlusion pressure, PA diastolic-occlusion pressure gradient, cardiac output, systemic and pulmonary vascular resistances) were compared between cohorts. Other than differences in the PA diastolic-occlusion pressure gradients, no significant differences were identified between cohorts. Pulmonary embolism patients were found to have increased PA diastolic-occlusion pressure gradients (10 +/- 5 vs. 3 +/- 2 mm Hg for the critically ill controls [p < .0002], and 4 +/- 4 mm Hg for the coronary artery disease cohort [p < .0005]). However, no significant difference in PA diastolic-occlusion pressure gradient values was identified when patients with proven pulmonary embolism were compared with patients in whom pulmonary embolism was clinically suspected yet not confirmed by angiograms (10 +/- 9 mm Hg; NS). For three of 19 pulmonary embolism patients, no occlusion pressure could be obtained due to an inability to wedge the balloon tip; 13 of 16 patients had PA diastolic-occlusion pressure gradients of > or = 8 mm Hg. In the pulmonary embolism cohort, PA diastolic-occlusion pressure gradient correlated well with pulmonary vascular resistance (r2 = .50; p < .05), but not with cardiac output or heart rate. CONCLUSION: In the large number of patients with right heart catheters in whom the question of pulmonary embolism is raised, an increased PA diastolic-occlusion pressure gradient (especially > or = 8 mm Hg) may provide a clue to the diagnosis of pulmonary embolism, but is not specific for this diagnosis.

Acute Disease↗
PubMed1995

Effect of cooling on oxygen consumption in febrile critically ill patients.

Hyperthermic critically ill patients are commonly cooled to reduce their oxygen consumption (VO2). However, no previous studies in febrile humans have measured VO2 during cooling. We cooled 12 febrile, critically ill, mechanically ventilated patients while measuring VO2 and CO2 production (VCO2) by analysis of inspired and expired gases. All patients were mechanically ventilated for hypoxemic, hypercapneic, or shock-related respiratory failure and had a mean APACHE II score of 22.4 +/- 7.7. As temperature was reduced from 39.4 +/- 0.8 to 37.0 +/- 0.5 degrees C, VO2 decreased from 359.0 +/- 65.0 to 295.1 +/- 57.3 ml/min (p < 0.01) and VCO2 decreased from 303.6 +/- 43.6 to 243.5 +/- 37.3 ml/min (p < 0.01). The respiratory quotient (RQ) did not change significantly, and calculated energy expenditure decreased from 2,481 +/- 426 to 1,990 +/- 33 kcal/day (p < 0.01). In 7 patients with right heart catheters, cardiac output decreased from 8.4 +/- 3.2 to 6.5 +/- 1.8 L/min (p < 0.01) as the oxygen extraction fraction also tended to decrease from a mean of 28.2 +/- 6.8 to 23.4 +/- 4.7% (p = 0.12) during cooling. Accordingly, cooling the febrile patient unloads the cardiorespiratory system and, in situations of limited oxygen delivery or hypoxemic respiratory failure, may thus facilitate resuscitation and minimize the potential for hypoxic tissue injury.

APACHE↗
PubMed1995

The effect of mechanical ventilation on oxygen consumption in critically ill patients.

We measured oxygen consumption (VO2) during spontaneous breathing with continuous positive airway pressure (CPAP), assist control ventilation (AC), and control ventilation during muscle relaxation (AC-MR) in eight patients undergoing resuscitation from cardiopulmonary failure. VO2 decreased in all eight patients between CPAP and AC-MR; mean VO2 (255 +/- 92 ml/min) on CPAP exceeded that on AC-MR (209 +/- 79 ml/min) (p < 0.005). Compared with CPAP, AC without MR reduced VO2 in five of eight patients and mean VO2 (227 +/- 59 ml/min) tended to decrease (p = 0.14); clinical examination did not distinguish patients requiring MR to reduce VO2 further. If VO2 on CPAP approximates VO2 during spontaneous breathing, the difference between CPAP and AC-MR (VO2resp) represents the decrement of VO2 that can be obtained during muscle rest. Both VO2resp and the mechanical work performed by the ventilator on the respiratory system were increased to about five times the efficiencies reported for normal patients, but VO2resp did not correlate with the mechanical work because of a wide range of respiratory muscle efficiencies. These efficiencies are less than those reported in normal patients, which may reflect the effect of sepsis, acidemia, hypoxia, or other conditions in these patients. We conclude that mechanical ventilation with muscle relaxation reduces VO2 by more than 20%; beyond stabilizing pulmonary gas exchange, these interventions preserve limited O2 delivery (QO2) for other vital organs.

Adult↗
PubMed1995

Heliox improves pulsus paradoxus and peak expiratory flow in nonintubated patients with severe asthma.

Heliox is a blend of helium and oxygen with a gas density less than that of air that decreases airway resistance (Raw) in patients ventilated for status asthmaticus. We tested whether breathing an 80:20 mixture of helium:oxygen would reduce pulsus paradoxus (PP) and increase peak expiratory flow (PEF) in patients presenting to the emergency room with an exacerbation of asthma. After receiving 30 min of beta-agonist aerosols and intravenously administered methylprednisolone, 27 patients whose PP remained greater than 15 mm Hg and whose PEF remained less than 250 L/min consented to breathe heliox or room air for 15 min. PP decreased and PEF increased with time in control patients, indicating a time-related effect of routine bronchodilator therapy (p < 0.05). PP decreased in 15 of 16 patients during heliox, and the change with heliox was significantly greater than that during air breathing (p < 0.01). PEF measured with a Wright's peak flow meter calibrated for heliox increased in all patients breathing heliox. Again, the increase in PEF during heliox breathing was significantly greater than the corresponding change in control patients breathing air (p < 0.001). To the extent that PP reflects the inspiratory fall in pleural pressure, this reduction in PP indicates a substantial reduction in inspiratory Raw when the less dense gas is inspired through narrowed bronchi having turbulent flow regimes. The 35% increase in PEF while breathing heliox signals a similar reduction in expiratory Raw, which might diminish the hyperinflation often observed during an exacerbation of asthma.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

The assessment and management of adults with status asthmaticus.

Despite advancing knowledge of the pathophysiology and treatment of asthma, asthma morbidity and mortality are on the rise. To help avert this trend, clinicians and patients must focus their attention on the early identification and treatment of asthma exacerbations. As in the words of Dr. Thomas Petty: " ... the best treatment of status asthmaticus is to treat it three days before it occurs." (7) Still, there will be asthmatics with life-threatening attacks that require careful assessment and aggressive management. Inhaled beta-agonists, systemic corticosteroids, and oxygen remain the drugs of choice in SA. Anticholinergics play a lesser role in the treatment of acute asthma, and debate continues regarding the efficacy of theophylline in this setting. Available data do not support the routine use of magnesium sulfate or antibiotics in patients with SA. Patients failing drug therapy should be considered early for intubation and mechanical ventilation. A strategy of mechanical ventilation that prolongs TE by limiting VE and decreasing inspiratory time, and that tolerates hypercapnia, avoids excessive lung hyperinflation and barotrauma and should improve the outcome of these most critically ill asthmatics. Intubated and mechanically ventilated patients should be aggressively sedated. Paralytic agents should be used only if adequate control of the cardiopulmonary status cannot be achieved by sedation alone. Minimizing the use of paralytic agents may decrease risk of myopathy and other adverse consequences of muscle paralysis. Finally, after successful treatment of a life-threatening episode of asthma, the treatment team should address prevention of future episodes of SA prior to discharge.

Humans↗
PubMed1995

Treatment of bronchospasm by metered-dose inhaler albuterol in mechanically ventilated patients.

beta 2-agonist bronchodilators delivered by metered-dose inhalers (MDI) are commonly used in the treatment of bronchospasm in both intubated and nonintubated patients. Substantial data support the effectiveness of MDI delivery systems in nonintubated patients. However, few studies have examined the effectiveness of MDIs in intubated, mechanically ventilated patients. MDIs are often used in conjunction with a spacing device that may enhance delivery of drug to the airways, but few in vivo data have demonstrated efficacy of this delivery method in ventilated patients. We studied ten critically ill patients who had a peak (Ppeak) to pause (Ppause) gradient of more than 15 cm H2O during sedated, quiet breathing on assist control ventilation. We administered 5, 10, and 15 puffs (90 micrograms per puff) of MDI albuterol through a specific spacer (Aerovent) at 30-min intervals, while measuring resistive pressure (defined as Ppeak-Ppause) before and after treatments. Resistive airway pressure after 5 puffs decreased in nine of ten patients, from 25.1 +/- 7.2 to 20.8 +/- 5.6 cm H2O (p < 0.12). The addition of 10 more puffs further reduced resistive pressure in nine of nine patients from 20.8 +/- 5.6 to 19.0 +/- 4.4 (p < 0.01). Fifteen more puffs (30 cumulative puffs) did not result in further improvement (p > 0.5). A toxic reaction occurred in one patient (systolic blood pressure decreased 20 mm Hg) after 5 puffs of albuterol. We conclude that MDI administered through this specific spacer is effective in mechanically ventilated patients in doses up to 15 puffs, and that therapy should be titrated to effectiveness and toxicity.

Administration, Inhalation↗
PubMed1995

Body composition and metabolic profiles associated with puberty in beef heifers.

Rapid growth large frame (RL, n = 61) or average growth medium frame (AM, n = 71) biotype heifers fed to achieve either moderate (MOD, .6 kg/d) or high ADG (HI, 1.0 kg/d) were used to determine whether puberty occurs at similar body composition or metabolic status. A heifer was considered pubertal after being detected in estrus and then forming a functional corpus luteum. Live animal estimates of body composition and blood samples for assessment of metabolic status were taken at 13 +/- .2 d after estrus for all heifers. Body composition and metabolic status were assessed every 56 d from 7 mo of age until puberty in a subset of 80 heifers representing all biotype-diet combinations. At puberty, 32 of these 80 heifers were slaughtered and physical and chemical composition of the empty body were determined. High-gain diet heifers were younger, heavier, taller, and more muscular (all P < .01) at puberty than MOD heifers. Slaughter measurements paralleled live animal estimates; bodies of HI and RL heifers contained more (P < .01) carcass and noncarcass components than those of MOD and AM heifers, respectively. Carcasses of RL and HI heifers were more (P < .05) muscular and fatter than AM and MOD heifers. At puberty, HI heifers had a greater (P < .01) mass of moisture, fat, and fat-free organic matter (FFOM) than MOD, whereas RL heifers had more moisture, ash, and FFOM than AM. Percentage of fat was greater (22.1 +/- 1.0 vs 1.0 vs 19.1 +/- 1.0; P < .05) and percentage of moisture was less (55.4 +/- .6 vs 58.1 +/- .6; P < .01) in bodies of HI than in those of MOD heifers. Concentrations of blood urea nitrogen and insulin were greater (P < .05) in HI than in MOD heifers. Diet did not influence concentration of IGF-I or glucose, and metabolic markers were unaffected by biotype. No dramatic changes in body composition or metabolic signals were detected before puberty. Puberty did not occur at similar body composition or metabolic status in all heifers.

Animals↗
PubMed1995

Improved synchrony, conception rate, and fecundity in postpartum suckled beef cows fed melengestrol acetate prior to prostaglandin F2 alpha.

Occurrence of estrus, conception rate, and fecundity were compared between postpartum suckled beef cows fed or not fed melengestrol acetate (MGA) before synchronizing estrus with prostaglandin F2 alpha (PG). One hundred thirty-three purebred Angus cows were stratified by age and days postpartum to one of two treatments. All cows received an injection containing 25 mg of PG; however, one group (MGA+PG) was fed .5 mg of MGA.cow-1.d-1 for 14 d then received PG 17 d after the last feeding of MGA. The other group (PG) received only PG. Cows in both treatments that failed to exhibit estrus within 6 d after PG received a second injection of PG 11 d after the first injection was administered. Cows were checked for estrus from the first PG injection until 6 d after the second PG injection. Cows were inseminated with semen from a 3/4 Brahman bull 12 h after observed estrus. Cows were exposed to Angus bulls after the AI period. Conception date was determined by palpation per rectum and verified by calving date and calf phenotype. Differences in response variables were analyzed by chi-square. A greater proportion of cows (P < .04) that were pretreated with MGA exhibited estrus after the first injection of PG (76%) than of cows that received only PG (60%). Total response did not differ between treatments after both injections of PG. Conception rate among cows that received a first service was higher (P < .007) for the MGA+PG (88%) group than for the PG (67%) group, although the total number of cows that received a first service was not different between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1994

Prospective randomized trial of LLETZ versus laser ablation in patients with cervical intraepithelial neoplasia.

Three hundred seventy-five patients with CIN on referral Pap and with a distinct cervical lesion on colposcopy were prospectively randomized to treatment with LLETZ or to standard colposcopic evaluation with directed cervical biopsies, endocervical curettage, and laser ablation of the transformation zone for biopsy proven CIN. Of the 195 patients that randomized to treatment with LLETZ, 32.5% had no evidence of dysplasia, 26.5% had CIN 1, 17.3% had CIN 2, 22.7% had CIN 3, and 0.5% had microinvasive carcinoma on final histologic evaluation. Of the 180 patients randomized to laser ablation, initial cervical biopsies demonstrated no evidence of dysplasia in 52.8% of patients, CIN 1 in 22.0%, CIN 2 in 18.3%, and CIN 3 in 5.7%. Only 114 (63.3%) of the women in the laser group required therapy. Complications were comparable for each treatment arm. Only 6.7% of patients randomized to LLETZ and 4.4% with laser ablation had persistent CIN on follow-up Pap. LLETZ appears to be effective, well tolerated, and less expensive, but the cost savings advantage of LLETZ over laser ablation may not apply to patients with CIN 1 on referral Pap smear since many do not require treatment.

Adolescent↗
PubMed1994

LLETZ is an acceptable alternative to diagnostic cold-knife conization.

Large loop excision of the transformation zone (LLETZ) provides a pathologic specimen similar to a cold-knife cone (CKC) biopsy of the cervix. One hundred twenty women with indications for a cone biopsy were evaluated with LLETZ to determine if this procedure is an acceptable alternative to traditional cold-knife conization of the cervix. All patients had LLETZ performed in the clinic under local anesthesia. An average of 2.1 slices was required to remove the transformation zone. Coagulation artifact interfered with histologic diagnosis in only 1.8% of specimens. The number of slices taken during the LLETZ procedure significantly correlated with the amount of heat artifact in the pathology specimen (P = 0.02) and interfered with the ability of the pathologist to determine complete excision of dysplasia (P = 0.03). LLETZ is an acceptable alternative to diagnostic CKC and can offer a substantial cost savings. To facilitate histopathologic interpretation, every effort should be made to minimize the number of slices and to maintain orientation of the LLETZ specimen. Endocervical curettage performed after LLETZ can identify a group of patients who are at high risk for CIN recurrence.

Adolescent↗
PubMed1994

Continuous intravenous infusions of lorazepam versus midazolam for sedation during mechanical ventilatory support: a prospective, randomized study.

OBJECTIVE: To evaluate the efficacy of continuous infusions of lorazepam vs. midazolam for sedation in the intensive care unit (ICU). DESIGN: Prospective, randomized study. SETTING: Large, urban university hospital. PATIENTS: Twenty adult medical ICU patients receiving mechanical ventilatory support. INTERVENTIONS: Patients were randomized to receive either lorazepam or midazolam. The infusion rate was adjusted at the bedside by the ICU nurse according to a standardized study protocol to achieve and maintain sedation at Ramsay's sedation level 2 or 3. MEASUREMENTS AND MAIN RESULTS: Ten patients were randomized to receive lorazepam and ten to receive midazolam. The groups were similar in demographics, Acute Physiology and Chronic Health Evaluation (APACHE) II scores, ICU admission diagnosis, underlying disease processes, and supplemental analgesic administration. The mean time to achieve initial adequate sedation was 124 mins for lorazepam and 105 mins for midazolam. The mean infusion rate at the point of initial sedation was 0.06 mg/kg/hr for lorazepam and 0.15 mg/kg/hr for midazolam. The maximum and mean infusion rates for the entire study period were 0.1 and 0.06 mg/kg/hr, respectively, for lorazepam and 0.29 and 0.24 mg/kg/hr, respectively, for midazolam. The number of infusion rate adjustments per day was 1.9 mg/kg/hr for lorazepam and 3.6 mg/kg/hr for midazolam. Of the surviving patients, the mean time to return to baseline mental status after discontinuation of the benzodiazepine infusion was 261 mins for lorazepam and 1815 mins for midazolam. The mean volume of fluid per day required to deliver the maximum dose of benzodiazepine was 1.2 L for lorazepam (maximum 2.4 L) and 1.3 L for midazolam (maximum 3.6 L). CONCLUSIONS: While there was a tendency to a longer time required for return to baseline mental status in patients receiving midazolam, this was not statistically significant. Findings of interest concerning both midazolam and lorazepam were: a) time to achieve sedation in medical ICU patients is often prolonged; b) actual dose requirements necessary to maintain sedation in this patient population are larger than the current literature describes; c) time to awaken after discontinuation of the infusion was occasionally delayed for > 24 hrs; d) large volumes of fluid were required to deliver these doses of drug via this route of administration.

Adult↗
PubMed1994

Cardiovascular physiology teaching: computer simulations vs. animal demonstrations.

The roots of physiology lie in laboratory observation, and physiology courses continue to rely on laboratory observation to provide students with practical information to correlate with their developing base of conceptual knowledge. To this end, animal laboratories provide a functioning example of interactions among organ systems and a source of data for student analysis. However, there are continuing objections to using animals for teaching, and animal labs are costly in time and effort. As an alternative laboratory tool, computer software can simulate the operation of multiple organ systems: responses to interventions illustrate intrinsic organ behavior and integrated systems physiology. Advantages of software over animal studies include alteration of variables that are not easily changed in vivo, repeated interventions, and cost-effective hands-on student access. Nevertheless, simulations miss intangible aspects of experimental physiology, and results depend critically on the assumptions of the model. We used both computer and animal demonstrations in teaching cardiovascular physiology to first-year medical students. The students rated both highly, but the computer-based session received a higher rating. We believe that both forms of teaching have educational merit. At the introductory level, the computer appears to provide an effective alternative.

Animals↗
PubMed1994

Effects of recombinant bovine somatotropin and dietary energy intake on growth, secretion of luteinizing hormone, follicular development, and onset of puberty in beef heifers.

The effects of dietary energy and recombinant bovine somatotropin (bST) on pattern of LH release, follicular development, and onset of puberty were studied in 40 Angus heifers. At 7 mo of age, heifers were assigned to a 2 x 2 factorial experiment; the main effects were dietary energy (high [HDE]: 14.15 Mcal of ME/d or moderate [MDE]: 10.84 Mcal of ME/d) and somatotropin (bST; 350 mg every 2 wk or vehicle). Beginning at 9 mo of age, heifers were observed twice daily for estrous activity. From 10.5 to 12 mo of age, five heifers from each treatment group were selected for weekly ultrasound examination of ovarian structures and biweekly sequential blood sampling to determine concentrations of LH. Somatotropin treatment altered intermediary metabolism in a manner consistent with enhanced accretion of lean tissue and decreased deposition of fat. The HDE heifers were younger (P < .001) at puberty than the MDE heifers, but BW at puberty was not different among treatment groups. Age and body weight at puberty were not affected by bST. Frequency of LH pulses increased within the 10.5 to 12 mo of age sampling window in HDE-treated heifers but not in MDE heifers (dietary energy x month of age; P < .02). Secretion of LH was unaffected by bST. Ovaries of bST-treated heifers tended (P < .09) to have fewer follicles > 5 mm in diameter than those of vehicle-treated heifers. We conclude that chronic treatment with bST did not alter age at puberty or pattern of LH release in heifers and that even modest differences in energy intake influence the timing of the prepubertal increase in pulsatile LH release.

Animals↗