Bioactivity of prolactin isoforms: lactation and recovery of menses in nursing women.
To assess whether plasma prolactin (PRL) characteristics relate to lactogenesis and absence or presence of menstrual cycles, we measured bioactive PRL (BIO-PRL) using the Nb2 assay, immunoreactive PRL (IR-PRL) by radio-immunoassay, calculated equations describing the BIO-PRL-IR-PRL relationship and separated charged PRL isoforms (by chromatofocusing) in five amenorrhoeic and five cycling nursing women at 6 months postpartum and in 10 cycling non-nursing women. Plasma samples were drawn before and 30 min after a suckling episode at 0800, 1600 and 2400 h in nursing women and at the same hours in non-nursing women. BIO-PRL and IR-PRL concentrations were highest in amenorrhoeic nursing women, intermediate in cycling nursing women and lowest in cycling non-nursing women. The BIO-PRL-IR-PRL relationship shows that a given amount of IR-PRL corresponds to equivalent amounts of BIO-PRL in cycling nursing and cycling non-nursing women, and to a larger extent in amenorrhoeic nursing women. IR-PRL was present in plasma as several charge isoforms. Bioactive isoforms eluting at pH 6.0-5.1 were found in amenorrhoeic and cycling nursing women, reaching similar concentrations after suckling. Bioactive isoforms eluting at pH 7.0-6.1 were found only in amenorrhoeic nursing women. We speculate that isoforms eluting at pH 6.0-5.1 may play a role in lactation and isoforms eluting at pH 7.0-6.1, in lactational amenorrhoea.
Campino
C
C
Departamento de Endocrinología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile.
Torres
C
C
Ampuero
S
S
Díaz
S
S
González
G B
GB
Serón-Ferré
M
M
D000328:Adult; D001942:Breast Feeding; D005260:Female; D006801:Humans; D007774:Lactation / Q000502:physiology*; D008597:Menstrual Cycle / Q000502:physiology; D011388:Prolactin / Q000502:physiology*; D020033:Protein Isoforms / Q000502:physiology
D020033:Protein Isoforms; D011388:Prolactin