Heat acclimatization blunts copeptin responses to hypertonicity from dehydrating exercise in humans.

Acclimatization favors greater extracellular tonicity from lower sweat sodium, yet hyperosmolality may impair thermoregulation during heat stress. Enhanced secretion or action of vasopressin could mitigate this through increased free water retention. Aims were to determine responses of the vasopressin surrogate copeptin to dehydrating exercise and investigate its relationships with tonicity during short and long-term acclimatization. Twenty-three participants completed a structured exercise programme following arrival from a temperate to a hot climate. A Heat Tolerance Test (HTT) was conducted on Day-2, 6, 9 and 23, consisting of 60-min block-stepping at 50% VO2 peak, with no fluid intake. Resting sweat [Na+ ] was measured by iontophoresis. Changes in body mass (sweat loss), core temperature, heart rate, osmolality (serum and urine) and copeptin and aldosterone (plasma) were measured with each Test. From Day 2 to Day 23, sweat [Na+ ] decreased significantly (adjusted P < 0.05) and core temperature and heart rate fell. Over the same interval, HTT-associated excursions were increased for serum osmolality (5 [-1, 9] vs. 9 [5, 12] mosm·kg-1 ), did not differ for copeptin (9.6 [6.0, 15.0] vs. 7.9 [4.3, 14.7] pmol·L-1 ) and were reduced for aldosterone (602 [415, 946] vs. 347 [263, 537] pmol·L-1 ). Urine osmolality was unchanging and related consistently to copeptin at end-exercise, whereas the association between copeptin and serum osmolality was right-shifted (P = 0.0109) with acclimatization. Unchanging urine:serum osmolality argued against increased renal action of vasopressin. In conclusion, where exercise in the heat is performed without fluid replacement, heat acclimatization does not appear to enhance AVP-mediated free water retention in humans.

Neurological correlates of fetal cocaine exposure: transient hypertonia of infancy and early childhood.

OBJECTIVE: To assess whether prenatal cocaine exposure has any long-term effects on neurodevelopment. DESIGN: A prospective cohort study with examiners blind to drug exposure and human immunodeficiency virus (HIV) status. SUBJECTS: Of 144 high-risk infants enrolled in a perinatal HIV neurodevelopmental study, 119 (83%) infants with both neurological and urine toxicology measures were followed up to age 24 months. METHODS: Neurological and developmental assessments were analyzed at 6-month intervals grouped according to the presence of cocaine in urine toxicology: 51 infants were cocaine-positive. Adjusted odds ratios (ORs) and 95% confidence interval (CI) were obtained by logistic regression equations that adjusted for perinatal variables, including measures of fetal growth, gestation, HIV status, and infant toxicology results. SETTING: Harlem Hospital Center from 1988 to 1992. RESULTS: At age 6 months, 21 of 51 (41%) cocaine-positive children exhibited hypertonia of any type (hypertonic tetraparesis, hypertonic diparesis, and hypertonic hemiparesis) compared with 17 of 68 (25%) cocaine-negative infants (OR = 2.1, CI = 1.0-4.6). Cocaine-positive infants were four times more likely to show hypertonic tetraparesis (HTP) than cocaine-negative infants (OR = 4.0; CI = 1.5-10.8). The association remained significant in multivariate analyses. Hypertonia, consistent with cerebral palsy, diminished over time in both groups. In 97% of affected infants hypertonia resolved by 24 months. Arm hypertonia abated first; leg hypertonia remained in some children up to age 18 months. No differences in development scores between cocaine-positive and cocaine-negative were noted at any age interval. However, among cocaine-positive infants those with early HTP showed significantly lower mean developmental scores at 6 and 12 month compared to infants without HTP. CONCLUSION: Cocaine positivity urine toxicology at birth is associated with hypertonia during infancy. Such cocaine-induced effects are usually symmetrical, transient, and the majority of exposed children outgrow hypertonia by 24 months of life. Among cocaine-positive infants, HTP may be a marker for later developmental impairments.

Intrapartum hypoxia: the association between neurological assessment of damage and abnormal excretion of ATP metabolites.

A series of 29 newborn infants had been studied after intrapartum hypoxia defined as meconium aspiration, an Apgar score of less than or equal to 6 at 5 min or a peripheral blood pH of 7.2 or less after resuscitation. Two independent sets of techniques were used; one concerned with the critical system in hypoxic damage, the central nervous system, the other assessing the central biochemical events in hypoxia. Both sets of data were assembled, then graded separately and only then combined. In this way detailed neurological assessment has been combined with measurement of urinary excretion of the ATP metabolites, hypoxanthine and xanthine. The essential metabolic consequence of hypoxia is a reduction in the synthesis of the energy currency of cells, ATP. This is associated with an outflow of ATP metabolites from cells. The extent of neurological damage was related to the magnitude of the hypoxanthine and xanthine excretion; neither were closely related to the initial blood pH. Infants who were normal neurologically had normal oxypurine excretion. Infants with neurological abnormalities for less than 48 h had lower excretion than those who were abnormal for more than 48 h. The duration of abnormal oxypurine excretion after an acute episode of hypoxia was studied in two infants with respiratory distress and in two other infants with apnoeic attacks. Severe hypoxia was followed by abnormal oxypurine excretion for at least 40 h after an acute episode. It is justifiable to suggest that abnormalities of oxypurine excretion should indicate intrapartum hypoxia in newborn infants. This excretion should also quantify the metabolic damage.