Breast growth and the urinary excretion of lactose during human pregnancy and early lactation: endocrine relationships.

Breast volume and morphology of eight subjects were measured before conception and at intervals throughout pregnancy until 1 month of lactation. Breast volume before conception ranged from 293 to 964 ml. At the end of pregnancy the volume of breast tissue had increased by 145+/-19 ml (mean+/-S.E.M., n = 13 breasts, range 12-227 ml) with a further increase to 211+/-16 ml (n = 12 breasts, range 129-320 ml) by 1 month of lactation. Urinary excretion of lactose increased at 22 weeks of pregnancy, signalling the capacity of the breast to synthesize lactose at this time. During pregnancy, both the change in breast volume and the change in cross-sectional area of the areola were related to the concentration of human placental lactogen in the plasma. The growth of the nipple and the rate of excretion of lactose were related to the concentration of prolactin in the plasma. During the first 3 days after birth, the rate of excretion of lactose was related to the rate of excretion of progesterone. There was no relationship between the growth of the breast during pregnancy and the amount of milk produced at 1 month of lactation.

Breast volume and milk production during extended lactation in women.

Quantitative measurements were made of relative breast volume and milk production from 1 month of lactation until 3 months after weaning, and the storage capacity of the breasts was calculated. The increase in breast tissue volume from before conception until 1 month of lactation was maintained for the first 6 months of lactation (means+/-S.E.M.) (190.3+/-13.1 ml, number of breasts, nb = 46). During this period of exclusive breast-feeding, 24 h milk production from each breast remained relatively constant (453.6+/-201 g, nb = 48), and storage capacity was 209.9+/-11.0 ml (nb = 46). After 6 months, breast volume, milk production and storage capacity all decreased. There was a relationship between 24 h milk production and the storage capacity of the breasts, and these both appeared to be responding to infant demand for milk. At 15 months of lactation, the 24 h milk production of each breast was substantial (208.0+/-56.7 g, nb = 6), even though the breasts had returned to preconception size. This was associated with an apparent increased efficiency of the breast (milk production per unit breast tissue) after 6 months, which may have been due to redistribution of tissues within the breast. The possible causes of the decrease in breast volume are discussed.

Blood and milk prolactin and the rate of milk synthesis in women.

In women, the concentration of prolactin in the plasma increases in response to nipple stimulation. This response has led to the assumption that prolactin influences the rate of milk synthesis. To investigate this hypothesis we have measured 24 h milk production, the short-term (between breastfeeds) rates of milk synthesis and the concentration of prolactin in the blood and breastmilk, from 1 to 6 months of lactation in eleven women. Over the long term, the 24 h milk production remained constant (means +/- S.E.M.): 708 +/- 54.7 g/24 h (n = 11) and 742 +/- 79.4 g/24 h (n = 9) at 1 and 6 months, respectively. The average short-term rate of milk synthesis (calculated from the increase in breast volume between breastfeeds; means +/- S.E.M.) did not change: 23 +/- 3.5 ml/h (n = 23) and 23 +/- 3.4 ml/h (n = 21) at 1 and 6 months, respectively. However, significant variation in the short-term rate of milk synthesis (from < 5.8 to 90 ml/h) was found both between breasts, measured concurrently (coefficient of variation, c.v. = 72%), and within the same breast, measured over consecutive breastfeeds (c.v. = 85%). The basal and suckling-stimulated concentrations of prolactin in the plasma (means +/- S.E.M.) declined from 1 to 6 months (basal, from 119 +/- 93 to 59 +/- 29 micrograms/1; peak, from 286 +/- 109 to 91 +/- 44 micrograms/l). In contrast, the concentration of prolactin in milk was much lower than in plasma, and decreased only slightly from 1 to 6 months of lactation (fore-milk, from 26.4 +/- 10 to 23.3 +/- 9.8 micrograms/l; hind-milk, from 18.9 +/- 5.1 to 13.2 +/- 6.3 micrograms/l). The concentration of prolactin in the milk was related to the degree of fullness of the breast, such that the concentration was highest when the breast was full. We found no relationship between the concentration of prolactin in the plasma and the rate of milk synthesis in either the short or long term. However, the relationship between the concentration of prolactin in milk and the degree of fullness of the breast suggests that the internalization of prolactin, after binding to its receptor, may be restricted when the alveolus is distended with milk.

Comparison of alphabetic and phonetic retrieval of online drug information.

Alphabetic, phonetic, and combined alphabetic and phonetic methods of retrieving online drug information were compared. Twenty-four volunteers participated in the study representing four user groups: physicians, nurses, pharmacists, and nonhealth-care hospital staff. Each subject performed 150 searches, 50 by each retrieval method. Using the alphabetic method, drug information was retrievable only if the drug name was spelled correctly. Using the phonetic method, searches were conducted based on the phonetic spelling of requests (e.g., "symetadine" for cimetidine). The combined method used a phonetic search only after an initial alphabetic search was unsuccessful. The elapsed time between the first entry and an indication that the information had been found or could not be found was determined, and the number of drug names not found and the number of excess tries were counted. There were no significant differences in elapsed time among the three methods. Pharmacists had the shortest mean elapsed time and physicians the longest. The average number of excess tries using the phonetic system was a third of the number required using the alphabetic method. The number of drugs not found showed only slight differences among the three methods. The subjects found the desired information on the first try 67% of the time with the alphabetic method, 66% with the combined method, and 90% with the phonetic method. The phonetic method had an average of 75 matches versus 20 for the alphabetic and combined methods. These results support use of a combined alphabetic and phonetic system for retrieving drug information.