The in vitro effect of prolactin on the growth, motility and expression of prolactin receptors in larvae of Toxocara canis.

The in vitro effect of prolactin (PRL) on the growth and motility of Toxocara canis larvae was assessed. Additionally, the expression and location of prolactin receptors (PRL-Rs) were determined in the larvae. Larvae of T. canis were incubated with different concentrations of PRL for different periods of time. The stimulated larvae accelerated their enlargement and increased their motility. The mean percentage of PRL-R+ cells in non-stimulated larvae, measured by flow cytometry was 7.3±0.3%. Compared with non-stimulated larvae, the mean fluorescence intensity (p<0.05) increased in larvae incubated with 40ng/mL of PRL for 10 days. A 465-bp length fragment was amplified from larvae gDNA by PCR. The sequence of this fragment showed 99% similarity with the gene fragment that codes for the PRL-R of the domestic dog. A high concentration of PRL-Rs was immune-located in the posterior region of the larval intestine; therefore, the intestinal cells in this region were most likely the targets for this hormone. Based on these results, PRL-Rs were identified in T. canis larvae, and the in vitro stimulation with PRL increased the number of these receptors, accelerated the growth and modified the activity of larvae. All of the above suggest that T. canis larvae are evolutionarily adapted to recognize the PRL of their definitive host and furthermore might explain the reactivation of tissue-arrested larvae during the gestation of bitches, which does not occur in gestating females of other species.

[Factors related to the blood lead level in children 6 to 30 months old in the Prospective Lead Study in Mexico City]. / Factores relacionados con el nivel de plomo en sangre en niños de 6 a 30 meses de edad en el Estudio Prospectivo de Plomo en la Ciudad de México.

A majority of the sample of children (N = 160-121, ages 6-30 months) from the Mexico City Prospective Lead Study exceeds the lowest limit action level (10 micrograms/dl) of the Centers for Disease Control standards for childhood lead exposure. Over one-third of the sample at 18 months and 24 months exceeds the action level (15 micrograms/dl) for aggressive intervention. Diet plays an important role in regulating early childhood blood lead levels. Fresh milk and breast feeding are associated with lower lead levels, but extended breast feeding is related to elevated lead levels. Low income and poor maternal education are associated with higher lead concentration in children. Child consumption of canned milk and juice, up to this date, is associated with elevated child lead levels. Canned products sealed with lead are disappearing from Mexican markets. Efforts to improve childhood nutrition and poverty may be expected to have the additional benefit of lowering lead levels of Mexican children.