Inhibitory respiratory responses to progesterone and allopregnanolone in newborn rats chronically treated with caffeine

Abstract

Key pointsr In premature newborns, recurrent apnoea is systematically treated with caffeine to prevent long-term neurocognitive disorders, but a substantial percentage of apnoea persists particularly in neonates born before 28 weeks of gestation.r Progesterone has been proposed as a respiratory stimulant potentially suitable for the treatment of newborn apnoea persistent to caffeine. Accordingly we asked whether acute progesterone administration reduces apnoea frequency in newborn rats treated with caffeine.r Surprisingly our results show that in newborn rats treated with caffeine, administration of progesterone inhibits breathing and increases apnoea frequency.r Additional experiments showed an enhanced GABAergic inhibitory drive on breathing after caffeine treatment, and that progesterone is converted to allopregnanolone (an allosteric modulator of GABA A receptors) to inhibit breathing.r We conclude that combining progesterone and chronic caffeine is not an option in preterm neonates, unless the effects of allopregnanolone can be counteracted.Abstract Caffeine is the main treatment for apnoea in preterm neonates, but its interactions with other respiratory stimulants like progesterone are unknown. We tested the hypothesis that the addition of progesterone to caffeine treatments further stimulates ventilation. Newborn rats were treated with water (control) or caffeine (15 mg kg −1 ) by daily gavage between postnatal day (P)3 and P12. At P4 and P12, we measured apnoea frequency, ventilatory responses and metabolic parameters under both normoxia and hypoxia (12% O 2 , 20 min) following an acute administration of either saline or progesterone (4 mg kg −1 ; I.P.). Progesterone injection increased the serum levels of both progesterone and its neuroactive metabolite allopregnanolone. Progesterone had no effect on ventilation in control rats under normoxia. Progesterone depressed ventilation in P12 caffeine-treated rats under normoxia and hypoxia and increased apnoea frequency in both P4 and P12 rats. Because allopregnanolone is an allosteric modulator of GABA A receptors and caffeine may enhance GABAergic inhibition in newborns, we studied the effects of the GABA A receptor antagonist bicuculline at 0, 1, 2 and 3 mg kg −1 doses and allopregnanolone (10 mg kg −1 dose) in P12 rats. In caffeine-treated rats, bicuculline enhanced ventilation, while allopregnanolone decreased ventilation and increased total apnoea time. Progesterone had no effect on ventilation and apnoea frequency in caffeine-treated rats injected with finasteride, which blocks the conversion of progesterone to allopregnanolone. We conclude that combining progesterone and chronic caffeine therapy is not an option for the treatment of persistent apnoea in preterm neonates, unless the effects of allopregnanolone can be counteracted.

Respiratory regulation by steroids in newborn rats: a sex‐specific balance between allopregnanolone and progesterone receptors

“…; Uppari et al . ). For these experiments, progesterone was given at 4 mg kg −1 once a day between 08.00 and 09.00 h between postnatal days 3 and 12 [gavage volume: 0.05 ml (10 g body weight) −1 ].…”

“…; Uppari et al . ). Briefly, fresh air flowing through the chamber was set at 180 ml min −1 , and the temperature inside the chamber was maintained at 30°C using a temperature control system (TCAT‐2; Physitemp, Clifton, NJ, USA).…”

“…; Uppari et al . ). All signals were recorded using Spike2 software (Cambridge Electronic Design, Cambridge, UK) and stored on a computer for further analyses.…”

“…However, several important concerns about the underlying mechanisms and potential interactions of progesterone with caffeine (Uppari et al . ) remain to be investigated before a clinical role could be developed further.…”

Sex‐based differences in apnoea of prematurity: A retrospective cohort study

“…potentiates the inhibitory action of GABA on basal respiratory activity (Uppari, Joseph, & Bairam, 2016); an observation that was less evident in female rats . Subsequent work by the same group showed that the stimulatory effects of acute caffeine administration become more important with age.…”