Newborn tissue concentrations of bupivacaine following maternal epidural administration during labor in guinea pigs.

Newborn plasma concentrations of maternally administered bupivacaine are often measured, but it is unclear how well they reflect tissue concentrations. Bupivacaine (0.25%) was administered epidurally (0. 12 ml/kg) 10 min prior to labor induction in 6 term-pregnant guinea pigs. Plasma, brain, heart and liver samples were obtained for bupivacaine analysis from newborns (n = 22) after spontaneous delivery. Liver bupivacaine concentrations were 2-3 times greater than those in the plasma, brain, and heart. A similar pattern of tissue concentrations was seen in a smaller number of newborns delivered by cesarean section. Liver bupivacaine concentration decreased with drug-delivery interval in littermates, while heart and brain concentrations showed no relationship with drug-delivery interval. Blood gases of newborns reflected acidosis, which may have influenced tissue drug concentrations. Under conditions of the study, bupivacaine concentrations in heart and brain, potential sites of bupivacaine action, were lower than those observed in a peripheral blood sample.

Changes in plasma alpha 1-acid glycoprotein and albumin concentrations during late pregnancy in rhesus monkeys.

Plasma protein concentrations are an important determinant of maternal-fetal drug transfer in the perinatal period. Plasma concentrations of alpha 1-acid glycoprotein (AAGP) and albumin were measured in pregnant rhesus monkeys using radial immunodiffusion assays at weekly intervals during the third trimester (n = 12), at 3-day intervals in the 2 weeks prior to full term (n = 10), and at 0, 1, 12, and 60 h after birth (n = 4). AAGP concentrations increased significantly, and albumin concentrations decreased significantly, from weeks 13 to 21 gestation as well as from day 150 gestation to birth. No changes were seen in the postpartum period. AAGP and albumin concentrations were highly negatively correlated from day 150 gestation to birth. The data suggest that AAGP and albumin concentrations are jointly but inversely regulated by physiological or hormonal conditions that precede delivery.

Long-term epidural catheterization of rhesus macaques: loss of resistance technique.

A method was developed for implantation of epidural catheters in the pregnant rhesus macaque (Macaca mulatta) for subsequent drug delivery in the fully conscious animal at parturition. Catheters were placed into the epidural space of 23 pregnant monkeys and accessed via a subcutaneously implanted vascular access port. The loss-of-resistance technique, a simple nonsurgical (percutaneous) technique, was used to locate the epidural space. Placement was confirmed at surgery by contrast radiography. There were no perioperative complications, and complications associated with long-term catheterization were limited.

Response to maternal separation in infant guinea pigs exposed to intrapartum meperidine.

We investigated whether opiate analgesics as commonly administered to women during labor would affect later response to maternal separation in infant guinea pigs. Meperidine hydrochloride (10-15 mg/kg i.m.) was administered to late-pregnant guinea pigs 5 min prior to labor induction with oxytocin. On Day 11 or 12 postnatal, pup distress vocalizations, locomotor activity, and plasma cortisol were measured under one of two conditions: alone (alone in a novel environment for 30 min) or mother (with the dam in the novel environment). Female pups exposed to intrapartum meperidine emitted fewer vocalizations than controls in the alone condition. Plasma cortisol was higher in meperidine females in the alone condition than in controls at the end of the separation period, but the difference was not significant. There was no drug effect on vocalizations or cortisol in males. Neither test condition nor drug affected activity level. The data suggest that intrapartum opiates may alter separation-induced distress in female guinea pig infants.

Epidural catheter placement for testing of obstetrical analgesics in female guinea pigs.

The pregnant guinea pig may be a useful model for the study of drug effects in the newborn. A reliable technique for epidural catheterization in the guinea pig was developed to allow use of this model to evaluate the effects of epidural labor analgesics on neonates. Catheters were implanted in two open pilot animals and 19 time-dated pregnant animals on days 59 to 62 of gestation. After establishing a surgical plane of isoflurane-induced anesthesia, an incision was made over the dorsal lumbar part of the spine. The L3-4 intervertebral space was exposed to allow introduction of a caudally directed 27-gauge catheter into the epidural space. The catheter was capped and implanted subcutaneously, then the animal was allowed to recover from anesthesia. Catheter placement was evaluated, using a bupivacaine test dose in 17 animals and postmortem histologic examination in 20 animals. One animal died immediately after surgery. Epidural placement was confirmed histologically in 15 of 20 animals. Failed catheters were either subdural, with one catheter found to be penetrating the spinal cord (intraspinal), or intramuscular. Response to epidurally administered bupivacaine was variable but was typically characterized by normal alertness and ability to use the forelimbs; depression of the panniculus reflex in the dorsal lumbar region; and hind limb motor impairment, with ataxia, loss of the placing reflex, and a tendency to drag the hind limbs. Subdural placement was associated with CNS depression, recumbency, shallow breathing, and sensory block ascending to the level of the ears.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between plasminogen activator production and bovine embryo development in vitro.

The relationship of plasminogen activator (PA) production to cell stage, cell number and changes in overall diameter and zona pellucida thickness for bovine embryos developing in vitro was determined. Late morulae to blastocysts (n = 80) were collected nonsurgically from naturally mated, estrous-synchronized, superovulated crossbred beef cows. Embryos were cultured, one embryo per 25-microliters microdrop, for 6 d. At 24-h intervals, embryos were evaluated for stage of development and transferred to fresh microdrops; media were recovered for PA analysis. In addition, embryo diameter and zona pellucida thickness were measured with an ocular micrometer. Plasminogen activator production was determined using a caseinolytic assay with urokinase as the standard. Changes in diameter, zona pellucida thickness and PA production per 24-h interval for each embryo were plotted, and the graphs were cut out and weighed. Sixty-one embryos (76%) completed the hatching process. Total PA production was correlated positively (P less than .005) to embryonic size (r = .40), developmental stage (r = .35) and cell number (r = .35) and negatively, but weakly, correlated to zona pellucida thickness (r = -.13; P = .267). Hatched embryos produced more total PA than embryos that did not hatch (.140 +/- .011 vs .070 +/- .019 g; P less than .01). These results suggest that as embryonic size and cell number increase and development progresses, bovine embryos liberate more PA.

The effects of plasminogen on in vitro ovine embryo development.

Plasminogen activator production by ovine embryos and the effects of plasminogen on ovine embryo development and zona pellucida integrity were evaluated. Eight-cell to sixteen-cell embryos were cultured in Whitten's medium containing 0, 60, or 120 micrograms/ml plasminogen. Plasmin and plasminogen activator concentrations in the medium were determined by a caseinolytic assay. More blastocysts hatched in medium containing 60 and 120 micrograms/ml plasminogen (33 and 21%, respectively) than 0 microgram/ml plasminogen (0%; p less than 0.05). Zona pellucida dissolution time in acidified phosphate-buffered saline was less after incubation in medium with 60 and 120 micrograms/ml plasminogen (7.2 and 5.9 min, respectively) than 0 microgram/ml plasminogen (9.4 min; p less than 0.05). Plasminogen activator production was low until the morula stage, increased during morula-blastocyst transition, and remained elevated through blastocoelic expansion and hatching. Zona pellucida solubility, plasminogen activator production, and plasminogen conversion to plasmin increased as embryonic stage advanced; however, plasminogen activator production and plasmin conversion to plasmin were poorly correlated with zona pellucida solubility. The results indicate that ovine embryos produce plasminogen activator, and plasmin can increase zona pellucida solubility; however, other factors may also be involved in altering zona pellucida integrity prior to hatching.