Group | Sex | Clonidine (0.2 or 2.0 mg/kg) | Growth Hormone Releasing Factor | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Pre-Peak2-a | Peak2-b | Pre-Peak | Peak | ||||||||
Width | Height | Width | Height | Area | Width | Height | Width | Height | Area | ||
min | ng/ml | min | ng/ml | μg/min/ml | min | ng/ml | min | ng/ml | μg/min/ml | ||
Young | Female | <6 | 3 ± 12-c | 37 ± 82-d | 68 ± 15 | 0.88 ± 18 | <6 | N.D.2-e | 51 ± 8 | 108 ± 24 | 1.82 ± 38 |
Male | <6 | 1 ± 2 | 42 ± 12 | 158 ± 262-f | 2.13 ± 312-f | <6 | N.D. | 54 ± 16 | 178 ± 362-f | 3.30 ± 622-f | |
Middle-Aged | Female | 42 ± 10 | 6 ± 5 | 39 ± 8 | 79 ± 18 | 1.14 ± 0.23 | <6 | N.D. | 49 ± 6 | 75 ± 19 | 1.36 ± 31 |
Male | 83 ± 112-f | 3 ± 5 | 38 ± 9 | 141 ± 292-f | 1.83 ± 0.352-f | <6 | N.D. | 51 ± 12 | 137 ± 262-f | 2.48 ± 0.462-f | |
MSG | Female | N.D. | N.D. | N.D.2-g | N.D.2-g | N.D.2-g | <6 | N.D. | 46 ± 14 | 20 ± 62-g | 0.41 ± 0.152-g |
Male | 121 ± 192-f 2-g | 2 ± 2 | 18 ± 62-f 2-g | 42 ± 182-f 2-g | 0.30 ± 0.132-f 2-g | <6 | N.D. | 62 ± 9 | 49 ± 132-f 2-g | 1.01 ± 0.282-f 2-g |
Neonates were treated with either MSG (4 mg/g b.wt.) on alternate days from 1 through 9 of life or an equivalent amount of NaCl vehicle. Male and female rats were divided into three groups; young (∼3 months old) vehicle-treated, middle-aged (∼12 months old) vehicle-treated, and MSG-treated (∼12 months old). Seven to ten days following serial blood collection for determination of plasma growth hormone profiles (see Table 1), rats were intravenously injected with diethyldithiocarbamate (500 mg/kg b.wt.). Two hours later, rats received low-dose (0.2 mg/kg b.wt.) clonidine (the nonresponse of middle-aged vehicle- and MSG-treated rats are not presented in the table). After an additional 2 h, only middle-aged vehicle- and MSG-treated rats received a higher dose (2.0 mg/kg b.wt.) of clonidine as reported above. Three hours after the last clonidine treatment, the rats were intravenously injected with growth hormone-releasing factor (3 μg/kg b.wt.). Serial blood samples were obtained at 15-min intervals from 7:00 AM, when the diethyldithiocarbamate was administered, to 4:00 PM.
↵2-a The pre-peak extends from the time of secretagogue administration to initiation of the growth hormone peak.
↵2-b Peak characteristics are defined in the legend of Table 1.
↵2-c Each value is a mean ± S.D. (n ≥ 4 rats/treatment group).
↵2-d The peak is initiated some time between administration of the secretagogue and collection of the first plasma sample 5 to 6 min later.
↵2-e N.D., not detectable, but for statistical comparisons assigned a maximum value.
↵2-f P < 0.01 when compared with females of the same age and exposed to the same neonatal treatment.
↵2-g P < 0.01 when compared with middle-aged vehicle-treated rats of the same sex.