Minipuberty in born small for gestational age infants: A case control prospective pilot study

PURPOSE

To evaluate minipuberty (MP) in small for gestational age (SGA) infants, both preterm and full-term, during the first year of life.

METHODS

33 SGA healthy newborns (group A), 21 of which full-term (subgroup A1) and 12 preterm (A2) were enrolled. Control group (B) consisted of 27 AGA, 17 full-term (subgroup B1) and 10 preterm (B2) infants. Growth parameters, FSH, LH, and Estradiol (E2) or Testosterone (T) serum levels were monitored at 3, 6, and 12 months.

RESULTS

The gonadotropin surge reached greater increase of LH in males at 3 months and FSH in females at 3, 6 and 12 months (p < 0.001). In male infants: T at 3 months was higher in subgroup A2 vs A1(p = 0.001), and correlated negatively with gestational age (GA, p < 0.005), length and weight at birth (p < 0.05); LH was higher in subgroup B2 vs B1 at 6 months (p = 0.003), and in group A vs B at 12 months (p = 0.03). Females displayed higher E2 at 6 months in B2 vs B1 (p < 0.05), negatively correlated with GA and weight gain (p < 0.05); LH at 6 months was increased in A2 vs A1 (p = 0.03). Overall, preterm males displayed higher T at 3 months (p = 0.001), LH at 3, 6 and 12 months (p < 0.05), and LH/FSH ratio at 6 months (p = 0.001). Preterm females exhibited increased LH/FSH ratio at 3 and 6 months (p < 0.05).

CONCLUSIONS

Irrespectively of GA, MP occurred with a typical sexual dimorphism and exhibited sex-specific correlations between hormones and perinatal parameters. SGA condition and prematurity seemed to enhance and protract MP over time in both sexes.

A single GnRH challenge promotes paternal care, changing nestling growth for one day

Decades of comparative and experimental work suggest that testosterone (T) promotes mating effort at the expense of parental effort in many vertebrates. There is abundant evidence that T-mediated trade-offs span both evolutionary and seasonal timescales, as T is often higher in species or breeding stages with greater mating competition and lower in association with parental effort. However, it is less clear whether transient elevations in T within a male's own reactive scope can affect parental effort in the same way, with effects that are visible to natural selection. Here, we injected free-living male tree swallows (Tachycineta bicolor) with gonadotropin-releasing hormone (GnRH), thus temporarily maximizing T production within an individual's own limit. Passive loggers at each nest showed that GnRH-injected males provisioned more frequently than saline males for the subsequent day, and their offspring gained more mass during that time. The degree of offspring growth was positively correlated with the father's degree of T elevation, but provisioning was not proportional to changes in T, and GnRH- and saline-injected males did not differ in corticosterone secretion. These results suggest that prior knowledge of T-mediated trade-offs garnered from seasonal, evolutionary, and experimental research cannot necessarily be generalized to the timescale of transient fluctuations in T secretion within an individual. Instead, we propose that GnRH-induced T fluctuations may not result in visible trade-offs if selection has already sculpted an individual male's reactive scope based on his ability to handle the competing demands of mating and parental care.

Neuropeptidergic and Neuroendocrine Systems Underlying Eusociality and the Concomitant Social Regulation of Reproduction in Naked Mole-Rats: A Comparative Approach

The African mole-rat family (Bathyergidae) includes the first mammalian species identified as eusocial: naked mole-rats. Comparative studies of eusocial and solitary mole-rat species have identified differences in neuropeptidergic systems that may underlie the phenomenon of eusociality. These differences are found in the oxytocin, vasopressin and corticotrophin-releasing factor (CRF) systems within the nucleus accumbens, amygdala, bed nucleus of the stria terminalis and lateral septal nucleus. As a corollary of their eusociality, most naked mole-rats remain pre-pubertal throughout life because of the presence of the colony's only reproductive female, the queen. To elucidate the neuroendocrine mechanisms that mediate this social regulation of reproduction, research on the hypothalamo-pituitary-gonadal axis in naked mole-rats has identified differences between the many individuals that are reproductively suppressed and the few that are reproductively mature: the queen and her male consorts. These differences involve gonadal steroids, gonadotrophin-releasing hormone-1 (GnRH-1), kisspeptin, gonadotrophin-inhibitory hormone/RFamide-related peptide-3 (GnIH/RFRP-3) and prolactin. The comparative findings in eusocial and solitary mole-rat species are assessed with reference to a broad range of studies on other mammals.

Effect of Adequate Thyroid Hormone Replacement on the Hypothalamo-Pituitary-Gonadal Axis in Premenopausal Women with Primary Hypothyroidism

BACKGROUND

While the effects of thyroxine (T₄) replacement on improving gonadal function in hypothyroid men has been well documented, the same has not been adequately studied in hypothyroid premenopausal women.

METHODOLOGY

Premenopausal women with overt hypothyroidism (thyroid-stimulating hormone [TSH] > 15 IU/L) were tested in the early follicular phase of their natural menstrual cycles or after a progesterone challenge for gonadotropins, estradiol (E₂), and prolactin (PRL). They were then treated adequately with T₄ replacement and retested under similar circumstances for the same parameters ≥2 months after the restoration of euthyroidism.

RESULTS

Forty premenopausal hypothyroid women were evaluated at baseline and ≥2 months after adequate T₄ replacement. At baseline, there was an inverse correlation of the gonadotropins (luteinizing hormone [LH] and follicle-stimulating hormone [FSH]) and TSH, prolactin (PRL) and free T₄ (fT₄), and E₂ and PRL. After normalization of the thyroid function, there was a significant fall in PRL (p < 0.001) accompanied by a rise in serum E₂ (p < 0.001). There were no changes in the levels of the gonadotropins LH and FSH. The proportion of patients with hyperprolactinemia fell 5-fold, from 5/40 to 1/40. While there were 5 patients with low estrogen prior to treatment, there were none with hypoestrogenemia after treatment.

CONCLUSION

Hypothyroidism is associated with a reversible partial suppression of the hypothalamo-pituitary-gonadal axis in premenopausal women, demonstrated by lower E₂ along with a mild elevation of PRL. Treatment of hypothyroidism improves the level of estrogen and lowers the level of PRL.