Objective: To determine the effect of caesarean section on breast milk transfer (BMT) to the normal term infant over the first week of life. Method: A sample of 88 healthy nursing mothers who had a normal vaginal delivery, and 97 mothers who had a caesarean section were recruited from a teaching hospital. Mothers and midwives were instructed to weigh the infants before and after each feed throughout the study period using calibrated portable electronic scales. Results: The volume of milk transferred to infants born by caesarean section was significantly less than that transferred to infants born by normal vaginal delivery on days 2 to 5 (p < 0.05), but by day 6 there was no difference between the two groups (p = 0.08). The difference could not be explained by any of the maternal and infant variables measured. Birth weight was regained by day 6 in 40% of infants born vaginally compared with 20% in those born by caesarean section. Conclusion: There is a lag in the profile of the daily volume of breast milk transferred to infants delivered by caesarean section compared with those born by normal vaginal delivery. This study also challenges the widely followed schedules of milk volumes considered to be suitable for the term infant, which appear to be excessive, at least for the first four to five days post partum.T he effect of obstetric procedures on the transfer of breast milk from nursing mothers to their infants is not known. Anecdotal evidence suggests that variability in breast milk transfer (BMT) is dependent on the mode of delivery of the infant. BMT is a function of a finely tuned feedback mechanism, which is potentially susceptible to pharmacological, physical, and psychological manipulations of the mother and/or her infant.The effect of maternal opioids on newborn motor and respiratory behaviour is well documented. Nissen et al 1 have shown a delay in rooting and suckling behaviour in infants whose mothers received one modest dose of intramuscular pethidine in labour. These initial infant reflexes are considered pivotal in promoting BMT.The importance of maternal regional anaesthesia on the newborn's neurobehaviour is difficult to assess. There is no uniform neurobehavioural assessment tool, and changing anaesthetic protocols make it difficult to compare one study with another and relate them to continually evolving contemporary practice. Nevertheless, newborn effects have been reported. Scanlon et al, 2 using a combination of neurological tests, found that infants whose mothers received a continuous epidural block using lignocaine had lower motor scores, including rooting behaviour, than infants where a block was not used. This effect persisted for at least eight hours. However, the use of epidural bupivacaine did not appear to have the same effect in a later study by the same author. Study infants were similar to the non-medicated control group. Yet, using the neonatal behavioural assessment scale, Sepkoski et al 4 found that epidural bupivacaine did affect infant orientation and motor scores, even after...

We have examined the role of the renal sympathetic nerves in the renal blood flow (RBF) response to hemorrhage in seven conscious rabbits. Hemorrhage was produced by blood withdrawal at 1.35 ml ⋅ min−1 ⋅ kg−1for 20 min while RBF and renal sympathetic nerve activity (RSNA) were simultaneously measured. Hemorrhage was associated with a gradual increase in RSNA and decrease in RBF from the 4th min. In seven denervated animals, the resting RBF before hemorrhage was significantly greater (48 ± 1 vs. 31 ± 1 ml/min intact), and the decrease in RBF did not occur until arterial pressure also began to fall (8th min); however, the overall percentage change in RBF by 20 min of blood withdrawal was similar. Spectral analysis was used to identify the nature of the oscillations in each variable. Before hemorrhage, a rhythm at ∼0.3 Hz was observed in RSNA, although not in RBF, whose spectrogram was composed mostly of lower-frequency (<0.25 Hz) components. The denervated group of rabbits had similar frequency spectrums for RBF before hemorrhage. RSNA played a role in dampening the effect of oscillations in arterial pressure on RBF as the transfer gain between mean arterial pressure (MAP) and RBF for frequencies >0.25 Hz was significantly less in intact than denervated rabbits (0.83 ± 0.12 vs. 1.19 ± 0.10 ml ⋅ min−1 ⋅ mmHg−1). Furthermore, the coherence between MAP and RBF was also significantly higher in denervated rabbits, suggesting tighter coupling between the two variables in the absence of RSNA. Before the onset of significant decreases in arterial pressure (up to 10 min), there was an increase in the strength of oscillations centered around 0.3 Hz in RSNA. These were accompanied by increases in the spectral power of RBF at the same frequency. As arterial pressure fell in both groups of animals, the dominant rhythm to emerge in RBF was centered between 0.15 and 0.20 Hz and was present in intact and denervated rabbits. It is speculated that this is myogenic in origin. We conclude that RSNA can induce oscillations in RBF at 0.3 Hz, plays a significant role in altering the effect of oscillations in arterial pressure on RBF, and mediates a proportion of renal vasoconstriction during hemorrhage in conscious rabbits.

The role of renal sympathetic nerve activity (RSNA) in the physiological regulation of medullary blood flow (MBF) remains ill defined, yet regulation of MBF may be crucial to long-term arterial pressure regulation. To investigate the effects of reflex increases in RSNA on intrarenal blood flow distribution, we exposed pentobarbital sodium-anesthetized, artificially ventilated rabbits (n = 7) to progressive hypoxia while recording RSNA, cortical blood flow (CBF), and MBF using laser-Doppler flowmetry. Another group of animals with denervated kidneys (n = 6) underwent the same protocol. Progressive hypoxia (from room air to 16, 14, 12, and 10% inspired O(2)) significantly reduced arterial oxygen partial pressure (from 99 +/- 3 to 65 +/- 2, 51 +/- 2, 41 +/- 1, and 39 +/- 2 mmHg, respectively) and significantly increased RSNA (by 8 +/- 3, 44 +/- 25, 62 +/- 21, and 76 +/- 37%, respectively, compared with room air) without affecting mean arterial pressure. There were significant reductions in CBF (by 2 +/- 1, 5 +/- 2, 11 +/- 3, and 14 +/- 2%, respectively) in intact but not denervated rabbits. MBF was unaffected by hypoxia in either group. Thus moderate reflex increases in RSNA cause renal cortical vasoconstriction, but not at vascular sites regulating MBF.

To test whether renal sympathetic nerve activity (RSNA) can differentially regulate blood flow in the renal medulla (MBF) and cortex (CBF) of pentobarbital sodium-anesthetized rabbits, we electrically stimulated the renal nerves while recording total renal blood flow (RBF), CBF, and MBF. Three stimulation sequences were applied 1) varying amplitude (0.5-8 V), 2) varying frequency (0.5-8 Hz), and 3) a modulated sinusoidal pattern of varying frequency (0. 04-0.72 Hz). Increasing amplitude or frequency of stimulation progressively decreased all flow variables. RBF and CBF responded similarly, but MBF responded less. For example, 0.5-V stimulation decreased CBF by 20 +/- 9%, but MBF fell by only 4 +/- 6%. The amplitude of oscillations in all flow variables was progressively reduced as the frequency of sinusoidal stimulation was increased. An increased amplitude of oscillation was observed at 0.12 and 0.32 Hz in MBF and to a lesser extent RBF, but not CBF. MBF therefore appears to be less sensitive than CBF to the magnitude of RSNA, but it is more able to respond to these higher frequencies of neural stimulation.

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The factors responsible for the development of hypertension during chronic activation of intrarenal V1receptors are unknown. We therefore tested whether medullary interstitial infusion of the selective V1-receptor agonist [Phe2,Ile3,Orn8]vasopressin (V1 agonist) influences renal antihypertensive mechanisms initiated by increased renal perfusion pressure (RPP). In intact anesthetized rabbits, the V1 agonist (10 ng ⋅ kg−1 ⋅ min−1) reduced medullary perfusion by 36 ± 7%, whereas cortical perfusion was reduced by only 14 ± 2%. An extracorporeal circuit was used to increase RPP in a stepwise manner from 65 to 85, 110, 130, and 160 mmHg for consecutive 20-min periods. Increased RPP reduced mean arterial pressure by 35 ± 8% in vehicle-treated rabbits, but by only 10 ± 3% in V1agonist-treated rabbits. Simultaneously, pressure-diuresis-natriuresis was induced; urine flow and sodium excretion increased similarly in the two groups of rabbits, but hematocrit did not change. We suggest that the depressor response to increased RPP is mainly due to release of a putative renal medullary depressor hormone (RMDH). Suppression of the release and/or actions of RMDH may therefore contribute to the hypertensive effect of chronic V1receptor activation.

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